Ontario government biologists are looking at how they can modify some hydro dams to reverse a crashing decline in the numbers of the American eel.

The length of eels makes them particularly susceptible to the turbines in hydro dams. They are the only fish that has ever been observed leaving the water to go around a dam overland, but that unique ability hasn't been enough to save them.

The numbers of eels reaching the waters of the Ottawa River from their spawning grounds in the open ocean has fallen by about 99 per cent since the 1980s.

There has been an eel ladder on the R.H. Saunders Hydroelectric Dam in Cornwall since 1974, but most Ontario dams don't have one.

The Ontario Power Generation-operated hydro dam at Chats Falls, about 50 kilometres southwest of Ottawa, has been ordered to start public consultations to find a way to allow eels to pass through, around or over it unscathed.

The most likely options are something similar to the fish ladders that help spawning salmon cross dams, or a trap-and-transfer system that catches eels on one side and deposits them on the other.

Eels are considered a bellwether of a river system's health and they also have remarkable life story. The eels that swim in the Ottawa River are all females, and they were all born in the Sargasso Sea — the so-called Bermuda Triangle.

They come to Ontario to live for as long as 20 years, before returning to the Atlantic Ocean to spawn babies who will in turn return to the Ottawa River, provided they can get past the dams.