The Department of Natural Resources says there's hope that a chemical might help stop the spread of the invasive aquatic species that is fast spreading in Minnesota lakes. The DNR treated Rose Lake in Otter Tail County last fall, and two divers who scoured the lake this week did not find any zebra mussels.

A new treatment that was intended to kill zebra mussels in two Minnesota lakes was not successful. The Minnesota Department of Natural Resources used copper sulfate, a chemical used to treat swimmer's itch, to get rid of the invasive species in Lake Irene in Douglas County and Rose Lake in Otter Tail County.

The invasive species has now infested more than 60 lakes across the state, MPR reports. Minnesota has about 3,000 public access points to lakes and rivers, but the Minnesota DNR has only 118 inspectors charged with keeping invasive species out of the lakes and rivers. The DNR says about 20 percent of boaters they check are violating laws by not pulling boat plugs, draining water or removing weeds from their vessels.

Officials say the inspections will prevent further spread of invasive zebra mussels. The county board will have the final say and must find a funding source for the inspections -- estimated to cost $30,000 a year.

Property owners on three Carver County lakes are suing Minnesota DNR Commissioner Tom Landwehr. They argue that it's up to the state agency to develop an approach that will stop the spread of invasive zebra mussels. And they say Commissioner Landwehr has failed in that duty.

The Minnesota Department of Natural Resources said Thursday that they've started on a research project to discover an effective and environmentally safe means to control zebra mussels and protect aquatic ecosystems. The DNR said Zequanox is a natural product that was approved by the Environmental Protection Agency for use in controlling zebra and quagga mussels that attach, colonize and clog closed industrial water systems.

Several lake associations in Carver County wanted to force the DNR to set up a boat inspection station to keep the invasive mussels from spreading to new lakes. But the court agreed with the DNR, which says it is only authorized to set up the stations at boat launches.

Zebra mussels were first found in Lake Minnetonka in 2010, and the invasive species has already infested the waters of the metro-area lake, KARE 11 reports. The shelled pests have moved further and become more dense, and now inhabit roughly 80 to 90 percent of the lake, one expert says. KARE's Belinda Jensen takes a dive and offers this up-close look at the worsening problem.