A path to restoring a damaged waterway

In a hotly contested issue over a brook circuit that runs through multiple ponds across West Tisbury and Chilmark, a West Tisbury town committee has completed its findings after four years of active field work; it is recommending restoring a pond in the middle of town to its natural state. 

Islanders may immediately have an image of Mill Pond come to mind when they think of the West Tisbury body of water off Edgartown Road. The still, glass-like ripples against a looming tree line, birds circling each other and bobbing down for food, and even the rare otter sighting all make up the tapestry of the area. The pond has been a landmark of the town for generations. 

But according to the Mill Brook Watershed Committee, there’s a different story beneath the surface — one they believe needs to be addressed. They say aesthetics shouldn’t be the main takeaway from Islanders’ experience with nature, but that care of the species who live there takes precedence. 

The committee’s top suggestion is to remove spillway boards and a dam that has impeded the brook in recent history. The dam and spillways that block Mill Brook are manmade, and the evidence the committee collected finds the barriers cause temperatures in the pond to rise to levels that are inhospitable for the species living there. 

Eventually, the committee hopes, the Mill Pond will return to its free-flowing, stream state — the way it used to look hundreds of years ago. If the water is released from stagnancy, they say American brook lamprey, herring, trout, and eel will thrive once again. 

Mill Brook flows from water sources from North Road in Chilmark to State Road in West Tisbury, ending in Tisbury Great Pond. But Mill Pond is the only body of water in the circuit that is owned by the town of West Tisbury — the rest, where there are other impediments to stream flow, are on private property. Therefore the main focus of the committee’s latest information and future recommendations are based on Mill Pond. 

Based on field statistics that the committee — formed by the town select board in 2014 — reported during a public presentation this weekend, the highest recorded temperature on a five-day stretch in August was 84°, far hotter than is healthy for some fish. The temperature goal for a body of water like Mill Pond is 68°, taking into account the specific species that live there. Removal of the spillways, and then the dam, would bring the Mill Brook to a regulated temperature that the species could tolerate, according to the studies done so far. 

The presentation on Sunday, Feb. 23rd, was well attended. The West Tisbury library was full of concerned Islanders, some of whom have been passionately researching Mill Pond for more than 10 years. A few locals on the local watershed committee have been doing on-the-ground sampling and observation of the pond for even longer –– West Tisbury resident Prudy Burt among them. 

“What we tried to do — and what we did — is present the town with several options for management going forward,” Burt told The Times. “The impacts are too big to ignore here.”

Burt has been vocal about her conservation efforts on Mill Brook for more than 20 years. For much of that time, she’s received a lot of pushback from the local community. But from her standpoint, the scientific results speak for themselves. 

Her concern for the wildlife, insects, and longevity of the brook are paramount. “I understand the emotional attachment to the aesthetics of the pond,” Burt said. “[But there are] hundreds of herring milling around with nowhere to go. We’ve altered it for our own preference, and now all these species are impacted. I don’t underestimate the aesthetics, but I temper that with what I’ve learned about ecology.”

The presentation on Sunday focused on a few facets of the Mill Brook landscape: water quality, oxygen concentrations, streamflow measurements, and macroinvertebrate sampling. In an interdependent system such as a brook or pond, each quality informs the next. The dam impedes proper streamflow, which stagnates the water and creates higher temperatures. 

According to Beth Lambert, the director of the Massachusetts Division of Ecological Restoration, “Dams damage water quality, prevent fish and wildlife from moving upstream, and are a liability to their owners … The majority were constructed during the industrial revolution to power mills, and no longer serve their original purpose,” she said. The Mill Brook dam was built for the same reason, but the West Tisbury mill in question hasn’t been operational for a long time.

Lambert stated that a study done by her division on dam removal found that even minor dams can have huge impacts on water quality. “Two-thirds of sites studied had warmer stream temperatures downstream of dams, and one-third had lower dissolved oxygen levels,” she said in a statement. 

The dissolved oxygen concentration is affected by the standing water as well, leaving macroinvertebrate species to suffer the consequences. According to the committee, much of the findings led them to believe the dam should be removed — water-flow impediments were shown to be the cause of a lot of ecological disruption in the system. Their recommendation for the town is to start the process by removing the spillways, then the larger manmade obstructions. 

“When the temperature increases, it can throw the whole ecosystem off-balance,” committee member Julie Pringle stated. “Increased temperatures that are potentially lethal, combined with potentially lethal low oxygen levels, creates an inhospitable system for these species that live there.” 

But opponents to the Mill Pond dam removal plan — the Friends of Mill Pond Group — say it’s not just aesthetics that motivate them to look for a different course of action. Sean Conley, a member of the group that would prefer Mill Pond be cleaned and restored instead of going with the committee’s recommendations, said he believes phosphorus and other harmful chemicals could be released into the pond’s waters.

Conley, also a member of the Historic District Commission, believes the manmade dam isn’t the problem for the fish there. He said that it’s the result of rising temperatures due to climate change and stagnant water over time. He and his group believe if the dam were to be removed, not only would the water still be inhospitable for the fish species they’re trying to save, but the silt, soil, and other debris that have built up behind the dam would release into the greater pond area, eventually flowing to the connected Tisbury Great Pond. 

“We’re gonna lose the beautiful body of water we have and not gain anything. [The Watershed Committee] says it’s worth the risk,” Conley said. He doesn’t agree. 

For Burt, the risk is not doing anything to help the pond or its inhabitants. The rising temperatures are a central point of the committee’s findings, but they recommend a different course of action from what Conley has suggested.

Burt pointed out examples from other towns where projects like this have been completed to mitigate fears about spillway and dam removal. In Falmouth, a similar problem was tackled at Child’s River. Similar to Mill Pond, Child’s River was teeming with sea-run brook trout a hundred years ago. However, due to manmade dams and cranberry bogs throughout the river circuit, the brook trout were seriously affected, their numbers quickly dwindling. The town of Falmouth started a long restoration that involved the removal of the dams and revitalization of the area. It was the second project of its kind in the area, and Burt said the results speak for themselves — the brook trout have returned, and the project is seen as a success story in the town. A similar restoration project in Falmouth, the Coonamessett River, is also seen as a success. 

David Foster, Harvard professor, ecologist, and  local author, supports the restoration of Mill Brook and the surrounding area. “There’s no question that Mill Brook is compromised by these dams and by these structures,” he said. 

He acknowledged that while the solution of dam removal may seem simple, the next steps in the process of restoration would be complicated. Any toxins being released into the pond once the dams were removed, for example, would be unlikely due to the amount of further studies that must be done to get clearance for next steps. Especially since this is a project now in the hands of the Town of West Tisbury, any sudden changes would have to be vetted by experts. 

“It’s a kind of classic conundrum and a classic debate that goes on all across the world, which is, you take a majestic ecological feature, you use it historically for industrial and agricultural purposes, and when those purposes are done, you’re left with the legacies of that history that have altered the stream in major ways,” Foster expressed. “So you’ve got a compromised ecological system, which has great historical and romantic and aesthetic value to many people. And you’ve got many other people who are aligned, understanding its incredible ecological value.”