A second environmental group has filed notice that it will sue the United States government over the State of Maine's blockade of gaspereau on the St. Croix River.

The Conservation Law Foundation and Friends of Merrymeeting Bay allege the Environmental Protection Agency has failed to enforce federal laws designed to protect the river.

The annual migration of gaspereau usually peaks around Victoria Day. And this year, like every year since 1995, that migration will end at a U.S. dam upriver from St. Stephen.

A special Maine state law orders the fish ladder at a dam be closed to prevent the fish from migrating into their spawning lakes further upriver.

Ivy Frignoca, a staff attorney with the Conservation Law Foundation in Portland, Me., said the EPA failed to enforce its own Clean Water Act and is accusing it of not reviewing the state's decision to block the river to a native fish.

The suit asks the court to order the EPA to perform the review.

Frignoca said there is little chance Maine's law would stand up to what amounts to an environmental impact assessment.

"In my opinion, I think these laws violate the Clean Water Act," he said.

Ed Friedman, a chairperson with the Friends of Merrymeeting Bay, another environmental group, said his organization has formally notified the EPA of its intention to sue over Maine’s blockade of the river, which continues after 17 years.

"We are firmly committed to opening up this river," he said.

Maine has blocked the St. Croix River to prevent gaspereau from migrating to their spawning grounds since 1995.

The state is trying to keep native gaspereau out, claiming it is protecting the smallmouth bass, an introduced fish favoured by anglers.

When Maine blocked the river to gaspereau in 1995, there were more than two million of the small fish in the river.

The fish population has dropped significantly since the state's actions.