Bad news for those who love to fish for trout

As Rivers and Streams Warm, Human and Aquatic Life Impacted

By Rob Smith / ecoRI News staff

Rhode Islanders don’t traditionally think of their home state as being a river-rich one.

With 420 miles of coastline, a centuries-long history of fishing, quahogging, and sailing, and a rich tradition of seafood, it’s not hard to see why the state has garnered its Ocean State moniker.

But that’s only part of the state’s environment. Inland, away from the famous coastal areas, Rhode Island is rich with freshwater rivers, streams, and wetlands that provide important habitat for plants, animals, insects, and fish — waterways that are just as vulnerable to climate change and development as Narragansett Bay.

“It’s really the same issues we face in Narragansett Bay,” said Kate McPherson, riverkeeper for Save The Bay. “It’s just on the other side.”

The Wood River in particular is a delicate habitat. A major tributary of the Pawcatuck River, its course hugs much of the state’s western border, starting from headwaters in Connecticut swamps and running through Exeter, Richmond, and Hopkinton before flowing into the Pawcatuck, and ultimately the ocean. Nearly three-quarters of land in the river’s watershed, about 73%, is forested, with less than 10% developed.

With its clear waters and heavily forested banks that seem rare in a small, highly developed state like Rhode Island, the Wood River is a destination for recreation, popular with anglers, kayakers, swimmers, when the water is deep enough, and hikers. Rhode Island’s popular North-South Trail runs parallel to the river for much of its path. The Wood is also an important drinking water aquifer for residents in Hopkinton and Richmond.

The river is a key habitat for the state’s only native trout species, eastern brook trout, sometimes known as brook char. A freshwater fish, their bodies are traditionally a dark, olive-green color, with blue and red worm-like markings, and yellow spots toward their flanks.

They can grow up to a foot in length, but most brook trout will top out between 6 and 8 inches long. Female brook trout spawn eggs starting in the fall, and their diet is primarily carnivorous. They eat other fish, mollusks, crustaceans, and insects.

Brook trout are vulnerable to climate change, and especially the water temperature of the state’s rivers. They prefer clean, cold fresh water that is less than 68 degrees, but have been known to withstand temperatures above 72 degrees for short periods of time.

It’s their temperature tolerance that makes them a prime indicator species for state environmental scientists; if brook trout are doing well, the specific habitat as a whole is typically healthy. But as the water temperature rises, so do the stakes for wildlife.

“So if the water temperature is too high, it holds less dissolved oxygen, just like in Narragansett Bay,” McPherson said. “In low dissolved oxygen conditions, animals can suffocate, it gets too hot, they die. Hot water is really the thing that we are seeing [in] climate change.”

That’s something the state is keeping an eye on when it comes to cold-water streams. Brook trout and cold-water stream habitats are listed in DEM’s 2015 Wildlife Action Plan as vulnerable to climate change.

“The limited distribution and quantity of these habitats in Rhode Island makes them particularly fragile and susceptible,” according to the plan. “As air temperatures increase, the suitability of cold-water streams for critical species such as Brook Trout will decline.”

In worse-case scenarios, hot water is a killer. Twenty one years ago this month, tens of thousands of dead fish washed up on the shores of Greenwich Bay due to the biggest hypoxic event in the bay in almost a century. The summer heat and wastewater runoff into Greenwich Bay had reduced dissolved oxygen levels to all-time lows and killed up to a million menhaden, American eels, and crabs.

Water temperature is one of the metrics state environmental officials are keeping an eye on. Provisional data from the University of Rhode Island’s Watershed Watch, which collects water samples and data readings from volunteers, shows fresh and saltwater waterbodies have recorded poor dissolved oxygen 23 separate times so far this year.

The latest final temperature data from Watershed Watch, dating from the 2022 monitoring year, shows only a handful of waterbodies reaching stressful temperatures on average. Shallow readings, temperature measurements taken about a meter below the surface, show much higher temperatures, ranging from anywhere between 70 and 77 degrees, and even greater.

It’s just a small slice of the data offered by the program, which also monitors bacteria and other surface-water quality metrics as a whole. Maintaining water quality isn’t just important for fish and wildlife, it’s also important for humans. The Wood River feeds into an aquifer that Richmond and Hopkinton residents draw water from, and maintaining healthy fish species is key for anglers who fish for pleasure, or for food.

Temperature and nutrient loading can also play a role in spreading aquatic invasives; 29 river segments in Rhode Island contain at least one invasive plant. The most successful invasive? Variable milfoil and fanwort; the same invading plants that just as successfully take over ponds and lakes.

Invasives can choke out other wildlife from a waterbody, decreasing oxygen levels and lowering water quality. Anglers have fewer fish to catch, and for swimmers, kayakers, and boaters, if the invasives have spread enough, it can be impossible to use rivers or ponds for any kind of human use. The worst-case scenario is an aquatic plant called hydrilla. In Rhode Island it’s in only a few ponds, but the invasive weed’s notoriety grew exponentially after it took over large sections of the Connecticut River. Marinas and boaters reported access to local slips and docks was rendered impossible because of how thick hydrilla was.

For brook trout, DEM officials have taken great pains to protect their habitat from rising temperatures. The fish are helped by the fact that a good portion of the Wood River runs through the Arcadia Management Area, a DEM-owned area that is free and clear of development. The greatest threat to water temperature, at least in more rural places similar to where the Wood River runs, is the elimination of canopy cover, which allows more direct sunlight to reach the waters and add heat.

DEM fisheries biologist Corey Pelletier has run a Christmas tree collection program every year after the holidays since 2018. Each year DEM invites residents to drop off their used, conifer Christmas trees at a check station in the Arcadia Management Area to build revetments — submerged structures consisting of many trees built in a half-moon shape — to add habitat for cold-water brook trout. Pelletier places the structures almost exclusively in the Falls and Wood rivers, the best local habitat for trout.

“It’s mimicking the natural process of wood falling into rivers,” Pelletier told ecoRI News earlier this year. “Trees near the river would fall in anyway and start this process on its own.”

Pelletier said the program collected 435 trees after the most recent holiday, a record number for the collection program. It’s enough to build up to half a dozen new revetments, each structure using between 50 and 100 trees. Over time, the structures will decay in the river, but as they decay, they capture sediment to strengthen riverbanks.

Revetments also prevent erosion. Frequent storms, where a lot of rain falls in a short amount of time, result in riverbank erosion. The water comes faster than natural systems are able to handle it, and it also dumps a lot of nutrients and runoff into watersheds from developed areas.

“Decades ago, we used to get more consistent rain,” McPherson said. “But now flash floods hit the ground, and run off into our wetlands, rivers, streams, and drainage systems. Those drainage systems are designed to get stormwater off the roads or impervious surfaces as quickly as possible, but that’s what causes more erosive forces in watersheds that are generally more developed.”

It’s development and impervious surfaces that contribute to flash-flood conditions for streams, and historically it’s been a bigger threat to them than climate change. An impervious surface is any material that blocks stormwater from soaking into the ground: think of a roof or a paved road or parking lot. Instead, the runoff is funneled into stormwater infrastructure, which typically puts it into the nearest body of water.

It’s how climate change-fueled flash floods can erode banks, widen rivers, and degrade water quality. Water washing off impervious surfaces is also far more likely to pick up more pollutants that are already on the ground. Nutrients such as phosphorus and nitrogen can degrade water quality and provide food for aquatic invasive species; toxic blue-green algae is a typical result, especially in the summer.

“When you talk about water warming up,” said Pat McGee, a DEM fisheries biologist in the Division of Fish and Wildlife, “you’ve got a number of factors that have been affecting rivers for hundreds of years now.”

Part of that equation is impounded and dammed streams and rivers. Thanks to the state’s industrial heritage, Rhode Island has far more lakes and ponds than should occur naturally. During the 1700s and 1800s, the state dammed dozens of rivers to create ponds to power mills and factories.

These operations gradually left, but the lakes and ponds remain. Most of them are now hot spots for recreation, like Johnson’s Pond in Coventry, and host summer cottages that later turned to suburban homes built around the shores.

But impounded rivers present a real problem for aquatic habitats. Damming a stream means the water isn’t flowing, so temperatures can start to rise in the pond, and fish can’t move up and down the river toward more pleasing temperatures.

“Anytime you take a dam out, and take out that impoundment that is soaking up the solar radiation, that’s going to help all the habitat downstream,” McPherson said.

Not all dams can be removed, however. Some dams are legally orphaned, meaning no one knows who exactly owns the dam, or others don’t want the dam removed, and in other cases an impoundment cannot be removed because of historical significance, or the impact to local drinking water. Others support the recreational value of a pond.

McGee said when DEM has to settle for not removing a dam, the solution is to install a fish ladder or fish passage to allow aquatic animals to move up and downstream from the dam. The most common fish path in the state, said McGee, is a denil fishway.

“It’s like a concrete sluiceway with wooden baffles that essentially, very slowly create an incline for the fish to swim up to get them from below a dam to above a dam,” he said. “They are concrete structures, either through or placed at the side of the dam.”

Most river fish, such as herring or trout, in Rhode Island are only about a foot long, said McGee, but the fish passages often have to be much wider than that to accommodate that gradual incline to get above the dam.

“Most of them are about four feet wide,” McGee said. “They’re big structures, you can’t miss them. To get a fish over a 10-foot head height dam, the incline can only be so steep, so those fish need a lot of room.”

Streams and rivers in Rhode Island are also, conversely, drying up. During the hot summer months, more perennial rivers are going dry during drought years, causing segments of the rivers to be disconnected from each other. McPherson pinpointed some of the causes as culverts crossing road infrastructure.

“Anytime a road crosses a river or stream, there’s pipes under the road that convey the flow of the stream,” McPherson said. “I’ve been down in the rivers looking at those crossings, and I can tell you many if not most of them have perched culverts.”

A perched culvert is where the river is flowing lower than the lowest part of the culvert, leading to human-caused disconnected streams. Most fish species traveling up and down the state’s streams aren’t great jumpers; perched culverts can have a similar effect on species as streams impounded by dams.

“All the animals that might want to move to a more suitable habitat are having a more difficult time,” McPherson said.