Its tendrils slither toward the surface, sometimes advancing inches each day from the gloomy depths.

Heaps of the stuff, glistening in the summer sun, lie along the edge of Montrose Harbor — evidence of the so-far failed effort to defeat it. Just beneath the surface of the water, it swarms like giant tangles of swamp-green yarn.

“It’s terrible, It gets in the props. [It’s] all over the place,” said Ira Myerson, 69, who owns a 27-foot sailboat that’s been moored at Montrose since 1985.

He’s talking about an invasive weed, Eurasian water milfoil, that’s common along the lakefront but, for some reason, has choked the waters at Montrose the hardest this year.

Alex Marin, 37, spent two hours Tuesday heaving out mounds of the slimy green muck so he could take a ride on one of his jet skis.

“As soon as we cleaned as much as we could, I dropped one of the jet skis off. Sure enough, it got clogged,” Marin said.

Marin and Myerson both said they’re angry that more hasn’t been done to clear away the weeds. Each pays about $5,000 per season to moor a single boat.

“It was horrific,” Marin said. “The dock is a business. They accumulate money. They make money. It shouldn’t be our responsibility to get that cleared up.”

Weeds piled up Wednesday at Montrose Harbor. Some boaters say the growth, which has taken over large areas of the harbor, is the worst in recent memory, making it difficult for boaters to get their boats out of the harbor. | Stefano Esposito | Sun-Times

Scott Stevenson is the executive vice president of Westrec Marinas, the company that manages 10 harbors for the Chicago Park District. He said Wednesday that the weed is a problem at marinas all along the lake.

“It grows up from the bottom of the harbor and it grows incredibly fast, and especially thrives when the water is warm and clear,” Stevenson said. “If sunlight can get down to it, … it will grow inches a day when it’s at its peak.”

The weed has been a problem for the 20 years Westrec has managed the lakefront harbors, but Stevenson isn’t sure why it’s so bad at Montrose this summer.

Workers used an aquatic herbicide to try to control the weed in June, and crews in boats routinely scoop out the weed.

“It’s not working as well as we’d like it to,” Stevenson said. “It’s working in our other harbors.”

A few days ago, more herbicide hit the water at Montrose.

“We expect it be … better within the next few days,” Stevenson said. Boaters “should see a difference. We’re doing all the things we can to fix the problem right now.”

Myerson says it’s not enough.

“I know three people who have moved their boat,” he said, “and I’m thinking of going to Waukegan.”

Some boaters, frustrated by the city’s efforts to control the weeds at Montrose Harbor, have taken matters into their own hands. | Stefano Esposito| Sun-Times