POND
RESTORATION

Warner's Pond is Not Beyond Repair, it just needs to be restored through active pond management.

All living things and systems experience birth, growth, and physical and chemical changes that humans experience and refer to as "aging". Naturally occurring water bodies, as well as man-made lakes and ponds, are in various life cycle stages of aging and decay. This is true for all bodies of water in the region, and within Concord, including Warner's Pond.

The size and shape of the dam and its reservoir has shifted over time, but there has been a dam and a reservoir of water on the site now named Warner's Pond, in nearly the same location for over three centuries. Since it's beginnings the pond has been undergoing a natural process we know as aging, but is scientifically described as eutrophication. Eutrophication occurs naturally over long periods of time as lakes (or ponds) fill in with sediments, leading to an increase in shallow water plant growth and low dissolved oxygen levels in the pond.

Scientists and lake managers have developed water management plans to reverse the eutrophication process. In a sense, water management efforts can reset the clock by improving the health and longevity of an aquatic resource, and reversing the negative effects associated with eutrophication.

Warner's Pond is experiencing both natural and human caused contributions to eutrophication, but it is not in an advanced state of eutrophication. An advanced state of eutrophication is marked by harmful algae blooms, dead zones, and fish kills. None of these events are occurring at Warner's Pond. However, the pond is in distress and it is impacting the ecosystem and recreation, which is why the Town of Concord voted to undertake and fund a dredging project.

When the Town of Concord voted to purchase a seven acre parcel in 2018 on the northern edge of Warner's Pond with plans of turning it into a public park, it also did a feasibility study to dredge the Pond. The Town then completed the process of designing and permitting a dredging project as part of a pond restoration project. Permits were obtained by the Town to dredge 35,000 cubic yards (approximately 6 acres) in 2022. This was enough dredging to restore a portion of the pond for ecological and recreational purposes. The town also voted to put Community Preservation Act (CPA) funds towards the dredging project. In total, there was approximately $3 million set aside for dredging Warner's Pond. In its final stages, a single very costly bid for construction ended the project, and the Natural Resources Division decided to instead pursue dam removal as the solution to the problems of invasive aquatic plants and sediment buildup, which would permanently eliminate the Pond.

A Warner's Pond Task Force, overseen by the Town's Natural Resources Commission, has been created to better understand the issue and how to move forward. The Task Force will likely review the costly bid to better understand why it was so high, and why it effectively killed a longstanding and voted upon dredging project to improve the aquatic habitat and recreational opportunities at the pond.

What is dredging?

Dredging is the process of cleaning out the bed of a harbor, river, or other area of water by removing mud, sand, weeds, and rubbish with a dredge. Dredging maintains the holding capacity of a reservoir or lake, improves its water quality, and also improves aquatic habitat quality.

Based on recommendations in a 2012 Warner's Pond Watershed Management Plan it was determined that dredging is a feasible option at Warner's Pond. The pond's sediments tested as uncontaminated, and consists mostly of sand.

Furthermore, the 2012 management plan estimated the sediment accumulation rate at Warner's Pond and concluded that sediment refill, after dredging, is expected to take "several hundred years" and provided a more conservative estimation of "100-years". Either way, dredging would provide a very long project lifespan, spanning generations.

"Dredging could be an environmentally sound and feasible management approach if conducted during the winter months when wetland areas associated with the pond would be dormant." Water quality, recreational opportunities and ecological habitat at Warner's Pond would be improved by dredging because it:

creates more deep water habitat that benefits aquatic wildlife
creates open waters that are free of shallow water vegetation
reduces water temperatures
increases dissolved oxygen
reduces conditions preferred by invasive species

Resources:

Dredging

Restoration

North American
Lake Management
Society

NALMS

Our mission is a simple, but powerful one: to forge partnerships among citizens, scientists, and professionals to foster the management and protection of lakes and reservoirs … for today and tomorrow.

Learn More

What is a Pond Management Plan?

"Keeping your lakes, ponds, and fisheries

ecologically balanced and beautiful isn’t a one-time job.

It requires consistent, proactive care by highly trained

lake management professionals."

– Solitude Lake Management Company

According to the NALMS website: link

A lake and/or watershed management plan is a dynamic document that identifies goals and action items for the purpose of creating, protecting and/or maintaining desired conditions in a lake and its watershed for a given period of time. Each lake management plan is different, depending on the conditions of the lake (watershed) and the interests of the stakeholders involved. A lake management plan also provides a framework for future lake boards & users as to what issues have been addressed and how successful previous efforts were. Lake management plans can be created by lake associations, but are often best left to lake management professionals as there are usually a variety of complex and interrelated issues at play.

Although a lake management plan should be site-specific, there are certain topics that most plans address. These include (but aren’t limited to):

Lake information (depth, size, watershed, development, etc)
Aquatic species management
Aquatic invasive species management/control
Wildlife/fishery management
Nutrient budgeting
Shore protection
Water quality protection
Recreational management
Watershed management

Management Plan

Dam Rehabilitation

In 2006, Concord Residents voted (article #29) to rehabilitate the Warner's Pond dam because the reservoir it creates is a valued town resource that is worth preserving.

Smart Design

In 2005, Concord hired GZA GeoEnvironmental Inc. and Dufresne Group Consulting Engineers to rehabilitate the Warner's Pond Dam.

The dam was rebuilt to achieve the following benefits: presentation

Improve Dam Safety
Preserve Pond Resources
Provide Functional Water Controls (including seasonal and emergency draw downs)
Improve Water Quality in Auxiliary Spillway Area

Strategic Engineering
The dam was completed in 2008, and it has a couple of noteworthy features:

Auxiliary Spillway Feature

There is a pocket-park on Commonwealth Ave, right at the Pail Factory Bridge. This small park allows people to view the Warner’s Pond dam; it is an especially good vantage point for seeing the “auxiliary spillway” feature of the dam. The auxiliary spillway was engineered to help steer water under the Pail Factory bridge and to prevent flooding. It was discussed at the time of construction, that this feature could also be easily and affordably retrofitted for fish passage if/when migratory fish make it to this part of the watershed. A large portion of the auxiliary spillway already mimics a natural riffle, which fish could effectively swim up to reach the pond. Perhaps one day, migratory fish will be here, and the pocket park will become a popular place for witnessing their journey into Warner’s Pond to spawn. Pond restoration and management would make this Pond an amazing habitat for migratory fish. For now, residents and visitors can come to enjoy the sights and sounds of the auxiliary spillway's riffle.

Sluiceway Feature

One of the highly anticipated benefits of the rehabilitated dam was its "sluiceway feature", which provides the town with functional water control. On more than one occasion, pond management reports cited that a dam with draw down capabilities would help make invasive plant management more effective and affordable. For example, early herbicide tests at Warner's Pond showed that they could have better outcomes if the water level could be lowered in a controlled way for application. There are additional benefits to drawdown features such as flood control when the water is expected to be higher than usual and you want to avoid "overtopping" of the dam from unusually high waters.

Dam Removal

Dam removal is being proposed for dams that are in poor condition and at high risk for failing and causing risk to downstream homes, infrastructure and people. When Concord voted to reconstruct the dam, instead of removal, they ensured that the dam is in good condition and at low risk for failure. Routine dam inspections submitted to the state indicate that the Warner's Pond Dam is in good condition with no safety concerns. The last two inspection reports request that the dam be reclassified as a "low hazard" dam, meaning failure or misoperation would result in no probable loss of human life and low economic and/or environmental losses.

Auxiliary
Spillway

Sluiceway for
Controled Drawdowns

Preliminary
Dam Renderings

Big Picture
Fish Passage

"Restoring habitat connectivity is the key to helping diadromous fish populations reach their full potential and continue to support a healthy coastal ecosystem."

– NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION,

U.S. DEPARTMENT OF COMMERCE

NOAA website: link

There is a national interest in restoring migratory fish populations, which includes diadromous fish who live most of their lives in salt water, yet need to return to fresh water to spawn. River herring (alewife and blueback herring) are local fish that fall into this category; as such, they are a keystone species that helps to keep both marine and freshwater ecosystems vital. The national interest in restoring diadromous fish populations stems from wanting to do what is ethically and environmentally responsible, and, from wanting to protect a critical part of a huge fishing economy. As a keystone species, herring feed and sustain the larger, edible, lucrative fish upon which the fishing industry depends. As NOAA's website explains, fishing for industry and sport has been part of New England's economy and culture for over 400 years (link). Before European settlement, these fish were an essential part of Native Peoples' diets. The world and the fishing industry are now far from this point in time, yet we need to learn from past practices, and find ways to live in greater balance, to sustain our lives with less negative impact on the intricate ecosystems that make life possible.

What's killing the diadromous fish?

Ocean Trawling & River Barriers

More recent, large scale fishing practices such as trawling have devastated herring populations and are finally coming under review. Some trawling restrictions have been put into place; however, they still do great damage to fish populations. It is a challenging balance between protecting an industry and protecting fish populations that are in great decline. Plus it is difficult to oversee and enforce fishing regulations. (Article about impacts of trawling: Huge herring haul worries rival fishermen, environmentalists.)

Robert F. Bukaty - Fosters Daily Democrat

The Conservation Law Foundations explains: "Midwater trawlers, which are some of the largest vessels on the East Coast, can catch millions of herring in a single tow. This intense fishing in a small area can result in “localized depletion,” meaning that segment of the ocean ecosystem has no more herring. This leaves local predators, like tuna, striped bass, whales, and seabirds, without an important food source. The herring caught by these giant ships can’t even be sold as seafood – they get crushed in the nets and end up sold as low-quality bait."

Barriers in rivers (e.g. dams) are another potential problem diadromous fish encounter, especially if there is no fish ladder, or similar mechanism, that allows for their passage over the dam. These fish need to access inland spawning habitats that include ponds/lakes, areas of still water, and streams to breed. Without access to these areas, they cannot spawn and their population cannot sustain itself. This impact to diadromous fish passage makes it easy to understand why there is support to remove dams by wildlife specialists, and to modify dams so they can successfully allow for fish passage during spawning runs. (Note: This is one of the reasons why the dam that creates Warner's Pond was designed and engineered with an auxiliary spillway feature, so that is can be easily and affordably retrofitted for fish passage if/when migratory fish make it to this part of the watershed.)

In 2006, NOAA National Marine Fisheries Service listed river herring as a species of concern. "Herring Restoration offers the opportunity for organizations and communities to prioritize river herring recovery at the river, watershed, and regional scale that will ultimately contribute to coastwide benefits to herring populations. The portfolio of approaches employed by restoration practitioners includes strategies such as increasing public education and awareness, removing passage barriers to re-establish connectivity to spawning and rearing habitats, improving water quality and other habitat condition, and implementing science-based management measures, or more drastically, moratoria on fisheries throughout their ranges."

Warner's Pond Dam

The Warner's Pond's auxiliary spillway feature was designed and engineered to be easily and affordably retrofitted for fish passage. However, there are several downstream barriers that first need to be improved and created before this effort would make sense. Sadly, it is not clear that migratory fish will ever arrive at this point in the river, but if they do, it would be amazing to see them spawning in Warner's Pond!

What would make migratory fish in Concord Possible?

First, The Essex Dam in Lawrence, and other lower dams need to be improved for fish passage. Then, once migratory fish begin to reach the Talbot Mills Dam in Billerica at consistent and substantial numbers, it too will need to be removed or improved for diadromous fish passage. Lastly, The Concord River Diadromous Fish Restoration Feasibility Study created in 2016 states: "Successful passage at this site (Talbot Mills Dam) would open access to over 35 miles of diadromous fish habitat on the mainstem Concord, Assabet, and Sudbury Rivers, plus more than 100 miles of habitat on tributaries to these rivers and at least 260 acres of lacustrine habitat (not including areas that could be accessed with fish passage at additional upstream dams). Diadromous fish populations could potentially become self-sustaining in the Concord River system with the implementation of this alternative." This means that once migratory fish have access to inland spawning habitat beyond the Talbot Mills Dam, no more dams would be required to come down for migratory fish to sustain their population. Further dam improvements and removal for that purpose would be optional, but are not anticipated to be necessary for the health of migratory fish.

Local Picture
Fish Passage

Warner's Pond is part of the Merrimack watershed. When water leaves the Pond, it flows into Nashoba Brook which feeds the Assabet River, then the Concord River, and lastly the Merrimack River. The mouth of the Merrimack River, where the river ultimately reaches the Atlantic Ocean, is between the jetties for Plum Island Beach and Salisbury Beach. Unfortunately, fish that would migrate from the Atlantic Ocean up to Warner's Pond to spawn, face several barriers that currently prevent this possibility. However, if and when they make it, the Pond's auxiliary spillway feature can be easily and affordably retrofitted for fish passage.

To better understand and appreciate the obstacles that diadromous fish face in the Merrimack Watershed, review this document: Merrimack River Watershed. At the end, there is a recommendation that reads, "Continue to stock and monitor river herring in the Concord River. If substantial numbers consistently reach Talbot Mills Dam, a fishway should be considered at that site." Sadly, fish counts have not been growing at Billerica's Talbott Dam, and the trouble seems to be even further downstream in Lawrence – at the very first dam diadromous fish encounter, the Essex Dam.

"Migratory fish counts are conducted throughout the watershed annually. Over the past two years, we’ve seen a disturbing 97% decline in herring migrating past the first dam on the Merrimack, the Essex Dam in Lawrence. This dam impacts the entire watershed."

– THE VOICE OF THE MERRIMACK NEWSLETTER, NOVEMBER 2023

Merrimack River Watershed Council: link

"Unfortunately, our river faces many threats, including degrading fish passage. Currently, we have a minimal herring migration that is reliant on inadequate fish ladders and fish elevators at dam sites. These structures can’t support a healthy fish migration and, recently, their failures have contributed to an alarming decline in herring migration."

The Essex Dam in Lawrence, Bjorn Lake/NOAA Fisheries

Hope

There are other watersheds in the Boston area that are faring better in the effort to expand fish passage for diadromous fish:

"The last time the Mystic River saw a dramatic increase in the herring population was the result of the construction of the fish ladder at the Mystic Lakes Dam in Medford. Horn Pond remains the next and last major water body in the Mystic River watershed that could offer new spawning habitat to herring, sustaining a larger total population."

– REPORT ON THE MYSTIC RIVER HERRING RUN 2023

Mystic River Watershed Website: link

"According to the official estimate from the Division of Marine Fisheries (Mass DMF), around 470,000 river herring passed through the fish ladder at the Mystic Lakes Dam in Medford in 2023 and around 12,000 herring made it into Horn Pond. This number represents a strong and stable population of river herring migrating through the Mystic River in 2023 amid fluctuations across the state. The next frontier for the expansion of the herring population is Horn Pond, a large body of water in Woburn, where a dam prevents many fish from accessing additional spawning habitat. Plans are underway to build fish passage at Horn Pond, using federal and local funding." (Article about urban fish passage: Our Urban Wildlife Migration.)

"With this exciting expansion on the horizon, it is possible that the Mystic could one day boast a million-herring run. We are incredibly thankful to the team of volunteers who have made all of this progress possible."

"The permanent solution was a fish ladder--a structure that provides "steps"--a series of small pools the fish can jump between. Now fish could pass freely from Lower Mystic Lake to Upper Mystic Lake for the first time in many decades."

A story-map that describes "The Great Return of Mystic Herring": Link

Fish Passage

POND RESTORATION

North American Lake Management Society