ST. PAUL, Minn. - The Minnesota DNR said it has ticketed more than 1,300 boaters for invasive species violations so far this year.

Conservation officers said the biggest concern is spreading zebra mussels because boaters are forgetting to drain their boats.

"They're so small that sometimes you can't see them with the naked eye," said DNR Officer Scott Arntzen.

The fine for violating DNR rules ranges from $100 to $500.