Fish in rivers rebound after dams removed
MISSOULA — Rivers rebound within a year after dams are taken out, an ecologist told scientists meeting in this city near Milltown Dam, targeted for removal.
Fish have exceeded expectations in re-establishing migratory routes, and it’s a myth that smelly mud flats are left in the former reservoir, Emily Stanley said Friday.
She studies the ecological effects of dam removal with her graduate students at the University of Wisconsin, and spoke at a workshop sponsored by the University of Montana.
Stanley warned that when a dam is taken out of a river, sediment is redistributed and that can bring trouble, at least in the short term, for some aquatic life downstream. She also said communities often lament loss of their backyard reservoir and the fish and wildlife it sustained.
Some of her comments were for state and federal regulators overseeing the planned removal of Milltown Dam on the Clark Fork River just east of Missoula.
“Within a month or two, the reservoir greens up,” she said, showing the newly green flats after removal of Rockdale Dam in southern Wisconsin.
“But for people who live on a reservoir, two months is too long. So we help nature along a little.”
On the Rockdale Mill Pond, state officials used a crop-duster to spread winter rye and prairie flower seeds. They saw results in less than two weeks.
Over time, vegetation grows in former reservoirs, but Stanley cautioned that what appears sometimes is non-native and weedy.
“In Wisconsin, the strategy has been to get the seed in early so it blocks the invasion,” she said. “Sometimes it works. Sometimes it doesn’t.”
Stanley has found fish studies positive.
On Wisconsin’s Baraboo River, where seven dams were taken out, migratory species re-established long-abandoned historic routes within a year. Eight of 16 migratory species not previously found above the dams were quickly traveling past the former blockades, Stanley said.
“There was this huge celebration when they saw the first river sturgeon migrate through Baraboo,” she said. “They hadn’t seen sturgeon there in 150 years.”
Fishermen were ecstatic, especially when the caddis flies and stoneflies returned “and the river remembered how to be a river,” Stanley said.
Not all fish migrate and the downstream movement of reservoir sediment “can hammer the resident fish,” she added.
“We still have an enormous amount to learn about fish. There are a lot of opportunities for research into their biology and behavior.”
Stanley cautioned that although dam-removal projects often are considered good, scientists and government officials must remember reservoirs have their proponents.
“While I like rivers, reservoirs are important to the people who live by them,” she said. “So don’t dismiss the significance of the event (dam removal) to those communities.”