Forget the zebra mussel. There's a new invader on Minnesota lakes that is taking over shorelines and threatening fish habitat.

It's the giant dock, a new aquatic species that comes in the wake of the oversized boat and the massive lake home.

"It's definitely becoming a greater issue," said Darrin Hoverson, a hydrologist with the Minnesota Department of Natural Resources (DNR) in Park Rapids. "We are seeing more and more folks trying to build platforms ... that are larger than the maximum of 170 square feet."

Monster docks are "popping up all over," said Paul Hoveness, a Minneapolis resident who's owned a cabin on Cross Lake near Brainerd for 35 years.

"People are putting these massive patios out on the lake," he said. "There are some of these platforms — oh, my God, they're 40 by 20 [feet], they've got tables and chairs and barbecue grills on the lake.

"In the old days you ran one piece of dock section out, just so you could get to your boat," Hoveness added. "Now it's become a recreational area for people to sunbathe and hang out. They just keep getting bigger and bigger."

DNR regulations limit dock platforms to either 120 or 170 square feet, based on the width of the walkway to the platform. Platforms larger than 170 square feet aren't permitted, but Hoverson said the DNR hasn't been aggressive about enforcing the limits.

Rather than writing tickets and ordering cabin owners to dismantle docks, DNR agents are giving dock owners information about the size regulations and asking them to set up their docks differently next year.

"Whenever we find these systems, we try to work with them to configure a dock that will be compliant," Hoverson said. "I try to use that annual install as an opportunity to say, 'Next year, configure it this way.' Enforcement action is very, very rare."

Hot spots for oversize docks include the Brainerd Lakes area as well as lakes close to the Twin Cities, Hoverson said.

The concerns about oversize docks are twofold, Hoverson said.

For one, large dock areas can interfere with natural shoreline vegetation and affect fish spawning areas. Studies have shown that docks and boat lifts may shade out important aquatic plants and eliminate critical habitat where fish spawn, feed and hide from predators.

There's a human component, too, he added.

"It's a privatization of the lake," Hoverson said. "The lake is a public water. So when somebody puts in a large platform or a large number of docks, that's where we really do see a conflict."

When large lakeshore decks proliferate, he said, "You feel like you're in a city on the lake. You don't feel like you're much in tune with nature anymore. We believe the large platforms are starting to shift that reasonableness to more disturbance on the lake."

The DNR regulations contain a loophole, however. As long as no section of the dock system is wider than 8 feet, a property owner can pretty much put up as much single-width dock walkway as they'd like. DNR officials sometimes refer to these extended, meandering walkways as "spider webs."

Hoverson recalled a cabin on Gull Lake that had one boat and a single dock platform of 200 square feet. That was illegal.

"His neighbor had five boats, all with U-shaped slips and [walkways] covering thousands of square feet," he said. "And that property was in compliance."

The DNR also has tried to educate dock sellers and installers about the size limits, Hoverson said, and the message seems to be hitting home.

"More people are aware of it now," said Craig Simard of Waterfront Services Inc. in Crosslake. "Years ago, people were building very large dock platforms out there. That's not so much the case now because people are aware of it.

"If they buy dock from us, we tell them. We don't want to sell them dock and have the DNR knocking on the door."

But Simard thinks the regulations could allow for slightly larger dock platforms.

"What bothers me is, someone who wants a 4-foot [walkway] going out and they want a platform at the end so their elderly parents can go out there, and the kids," he said. "And 120 square feet isn't enough.

"But you could have eight boat lifts covering the entire waterfront, and that's permitted."

John Reinan • 612-673-7402