Hydro dams are often blamed for the demise of eels in the Ottawa River, but a group of researchers has been trying to figure out a way to provide them a safe passage upstream.

About 98 per cent of the eel population has vanished from the Ottawa waterway over the years, making the slimy, slithering fish an endangered species. Turbines within the dams created a major barrier for eels as they travelled upstream — they would either be trapped or chopped up along their journey. 

The Canadian Wildlife Federation and the Ottawa Riverkeeper worked with Energy Ottawa to install new sets of turbines that create safe passage channels through dams on the Ottawa River, including the one at Chaudière Falls.

Now, to measure the effectiveness of the new turbines, the research group tagged and released more than 400 American eels Wednesday at Petrie Island Beach.

Researchers anesthetized the fish in order to tag them, which involved inserting a needle below the surface of the skin and inserting a tag. PVC-style pipes are used to carefully handle and measure the fish's length and weight. 

Researchers study eels at Ottawa River July 12, 2017

Researchers measure a young eel at Petrie Island Beach before releasing them into the Ottawa River. (Photo courtesy Martin Lipman/Ottawa Riverkeeper)

Carleton University master's student Sarah Walon tagged 12 young eels Wednesday. 

"Because of the fact that they are an endangered species we actually recommend that people do their best not to actually handle them," she told CBC Radio's Ottawa Morning. 

"So, yes, if people see an eel, if they do incidentally catch one, certainly take if off their hooks and return it as soon as possible. At least keep your hands wet. They do have a particular coating on them, a slime on them."

While eels are one of the most studied fish, there's still a lot to be learned about them, according to Nick Lapointe, Canadian Wildlife Federation senior conservation biologist and member of the research team. He helped release some of the eels back into the river. 

His team wants to know how far they travel, if they stay in the river, or go back to the St. Lawrence River where they were captured. Over time, researchers hope to be able to re-capture the eels and get the answers they're looking for. 

"Most are going to stay here in the river somewhere between Hawkesbury and Ottawa and they'll grow in the river for the next 20 to 40 or 50 years," said Lapointe.

"Eventually, once they're big enough [they will take] one trip back to Sargasso Sea near Bermuda to spawn and that's it," he said. "That's their lifecycles."

Tag and release eel into Ottawa River July 12, 2017

Researchers release eels into the Ottawa River on to learn more about them. (Photo courtesy Martin Lipman/Ottawa Riverkeeper)