Michael Flannery pilots an open top barge into the Bayou, a narrow dead end channel where the Songo River empties into Sebago Lake. As manager of the Lakes Environmental Association’s invasives program, he helped clear variable leaf milfoil from the waterway last summer.

“We left this last year looking pretty good, and now this year it is full of milfoil,” Flannery said.

Beneath and between boats crammed against the shore milfoil spreads in thick mats. It’s the most common, and problematic, aquatic invasive plant in Maine. Even a small fragment stuck on a boat hull or propeller could spread milfoil into another water body.

“We’ve been working already this year, we’ve removed a couple thousand pounds of milfoil already, but it is just starting,” Flannery said.

Left unaddressed, the milfoil will take over shorefronts and crowd out natives species of plants, fish and wildlife. Out of control infestations can ruin a lake for fishing, boating and swimming.

It’s also becoming harder to manage. Climate change driven by burning fossil fuels has warmed Maine lakes 5.5 degrees Fahrenheit on average since the 1980s, far faster than the annual air temperature increase. With warmer water and milder winters, lake ice doesn’t last as long.

That means a much longer growing season for plants than before.

“If the ice is gone in early march, the lake is going to warm up quicker, the stuff is going to start growing,” said Lakes Environmental Association executive director Colin Holme.

“We have milfoil growing earlier and it grows later into the season. There were reports of milfoil growing vibrantly into November last year,” Holme added.

To illustrate his point, Holme points to a patch of milfoil in the Bayou that’s already flowering above the water. That’s an indication of a robust plant with good prospects to reproduce.

“Most years it didn’t flower, and when it did flower it was a big thing, we’d go down, we’d photo document it. And now it is flowering most years, and this year it started flowering in June, which is unheard of. Usually its flowering is late July and August,” Holme said.

Once invasive plants are established, they’re nearly impossible to fully eradicate and expensive to contain.

John McPhedran, from the Maine Department of Environmental Protection, said the state is lucky to have an active network of volunteers and nonprofit organizations addressing invasives. Groups survey lakes, set up boat inspections at public launches, and do removal work.

“We’re fortunate to have that interest, that capacity,” McPhedran said. “And while the threats that come with a longer growing season are a real challenge, I think we’re in good stead to try and manage those as best we can.”

Only about 40 lakes and ponds in Maine have recorded invasive plants. That makes it an outlier compared to other states.

“We still have a lot to protect in Maine,” McPhedran said. “Other states have, I think, a much higher percentage of their waterbodies that have an aquatic invasive species.”

But advocates worry the bulwark against the spread of unwanted species is starting to buckle.

Courtesy boat inspectors are the first line of defense against invasive spread, by helping vessel owners check to see they’re not transmitting plants and educating the public about the problem.

But just like the growing season, the boating season is lasting longer too. And those launches are starting to go unattended.

“The boat launches are very, very busy in the fall, that’s when there’s a lot of bass tournaments, and just a lot of a lot of people enjoying leaf peeping season and all those things,” said Sharon Mann, director of the invasives program at Seven Lakes Alliance in Belgrade.

Public funding for courtesy inspectors is miniscule to begin with, Mann said. And after high school and college students hired to monitor the public launches leave around labor day, the group struggles to find replacements.

“We have ads posted year round for courtesy boat inspectors, but there just isn’t anyone to hire outside of Memorial Day to Labor Day,” Mann said. “And it really scares me how many boats are going uninspected in and out of these launches.”

Back on the Songo, Colin Holmes from the Lakes Environmental Association shows off a long section of river that has been mostly cleared of milfoil after years of effort.

The Songo is the busiest inland waterway in the state, increasing its infestation risk, he said.

The association used divers to hand-harvest milfoil and underwater barriers to keep it from growing. Even though the river is in better shape than it was, it takes annual suppression efforts to keep invasives at bay. In early July, two dive teams from Lakes Environmental Association were still searching the Songo for milfoil and pulling it where they could.

“It’s a success story in my mind and we are so lucky we started when we did,” Holme said. “I think if we started now, the water is so warm I don’t think we could get a handle on it.”

Success doesn’t come cheap. His group budgets about two hundred thousand dollars a year for invasive work. A state grant pays for a quarter, fundraising has to cover the rest.

“It’s expensive work, there’s a lot of liability, there’s a lot of training. It’s just not easy and people don’t understand how much it costs,” Holme said.

Lawmakers recently increased the price of “milfoil stickers” that owners get when they register boats with the state. That’s expected to raise funding for the invasive program to $3 million next year, a 60 percent boost.

The money should help, Holme said. But he also hopes people start paying attention and doing more to prevent further infestations, before it is too late.