Tolkkinen: Wakeboat operators need to watch this video

It doesn’t take much imagination to realize how fun wakeboats must be.

You bomb along on a sunny day, favorite tunes blasting, friends and family piled in the boat with a pal or a granddaughter surfing your wake, maybe not exactly how it’s done in California, but still amazingly cool for a landlocked state like Minnesota.

Unlike a faster, riskier sport like water skiing, wakesurfing is a relatively gentle lake activity. If you fall, you’re not likely to tear a muscle. You just sink gently into the water.

What is not so easy to imagine is those hidden worlds beneath the wakeboat. After wakeboats pass, the water closes back up, so the revelers have no idea about the destruction they cause below.

Until this week, the rest of us didn’t know, either.

Now we do. The University of Minnesota filmed it and, on Tuesday, released videos that every wakeboat owner, dealer, manufacturer, operator, and lake association should watch. They also released a study that recommends that wakeboats should not go at “semi-displacement mode” (the speed at which they churn the largest wakes) in less than 20 feet of water. That’s the minimum recommended depth. In places where plants grow along the lake bed, they should be 20 feet above the plants.

Researchers filmed lake beds to see what happens when wakeboats pass at depths of 9 feet and 14 feet of water at the speed that creates the most wake.

Things explode.

The sediment at the bottom rocks and flies apart as if struck by a tornado.

Plants rip away from the lake bed.

Water clarity vanishes, replaced by a rocking, drifting cloud of muddy particles that obscure the camera lens. Some of it continues to hang in the water for 15 minutes, until the boat passes over again and stirs it up even more.

You might think, big deal. The sediment subsides eventually. It’ll be fine.

“There’s a lot of nutrients in lake bottoms,” Riesgraf said. “You have aquatic vegetation, you have animals dying, and all that sinks to the bottom where it goes through various stages of decomposition.”

Stirring up the lake bed stirs up things like phosphorus that can lead to algae blooms on the lake surface. And that’s bad for everyone, including people who want to wakesurf. It probably also affects mussels and clams and other aquatic life in ways we don’t yet understand.

Don’t you sometimes shake your head at the destruction we unwittingly cause in the name of recreation? Snowmobiles must seem cataclysmic to the mice and voles that live in subnivean zones.

The study also looked at several smaller motorboats, and found that they, too, stirred up sediment. It’s not nearly as much as wakeboats, but it still bothers Jeff Forester. The executive director of Minnesota Lakes and Rivers Advocates uses a 1975 Boston Whaler to cross 11 miles of water to get to his property. It’s not a big boat, but he is newly aware that it can create havoc on the lake bed in shallower water.

“I can cause damage to the lake and drive algae blooms with that boat,” he said. “It gave me pause.”

People can be forgiven for not knowing. They’re out on the water, bonding with their families and their friends, having a great time. It’s not readily obvious that what they’re doing is harming the lake bed or leading to algae blooms or eating away at the shoreline.

Now we know.

What do we do next?

What will wakeboat operators do next?

Will they follow the research recommendations that when they are in surf mode, they stay 500 feet away from shoreline and other watercraft and in water that is at least 20 feet deep?

That means staying away from shallow, narrow lakes. It means watching the boat’s depth gauges. Some lakes that have lake associations are starting to post maps at boat ramps showing safe wakesurfing areas, which is a great tactic to ensure shared, mutually respectful use of the waters.

Probably many, maybe even most, of them will follow the guidance. Most Minnesotans are good people who want to do the right thing.

The problem is those who think they can do whatever they want because they’re Americans and it’s all about freedom and nobody can tell them what to do.