EAST GRAND FORKS, Minn. (AP) -- Inspectors for the state's aquatic invasive species program are struggling to keep up with the spread of zebra mussels in Minnesota lakes this summer.

Minnesota Public Radio News reports Monday that the invasive species has invaded more than 60 lakes across the state. While Minnesota has about 3,000 public access points to lakes and rivers, the Department of Natural Resources has only 118 inspectors charged with patrolling for invasive species.

Agency officials say about 20 percent of boaters they check are in violation of laws aimed at preventing invasive species. That means boats where owners have failed to pull plugs, drained water or removed weeds.

DNR Regional Supervisor Bruce Anspach says the agency has made progress in building awareness among boaters of preventing the spread of invasive species.