HAYDEN LAKE, Idaho – Idaho officials are dealing with an especially annoying problem in Hayden Lake this summer.

It is called milfoil. It is essentially an underwater weed that spreads fast. Experts said it has become worse in just the last couple years. The water-weeds ruined the day for Holly McKnee and her son.

"It's just thick and gross and you can't avoid it. We couldn't swim today. It was a bummer," said Holly McKnee, who planned to kayak on the lake Monday.

A headache for adventure-seekers and a hapless source of income for others. A private contractor has hired by homeowners to get rid of the milfoil near their docks.

Milfoil is an invasive species. It is not just gross, but it can muscle out other plants and make water more stagnant. It did not use to be this bad, either.

“Our dock, I can't swim at it anymore. I'm in 15 feet of water, and this milfoil is all the way to the surface,” said Merlin Thykeson, who has lived on the lake for 30 years.

A milfoil expert with the Idaho Department of Agriculture said the problem has certainly become worse in the last two years. The department is bringing in a contractor from Western Washington to help do some underwater weed-whacking. They will spray herbicide to help fight it, but that means some people who draw their water from the lake, like Thykeson, will not be able to drink it for a few days.

It is not entirely clear how it got this bad, but with more development in the area, more logging, and more boaters, people in the area said this is a major issue.