If you take a spin in the boat this holiday, make sure you don’t bring along some unwanted hitchhikers. Martin Conrad, a fisheries biologist with the Iowa Department of Natural Resources, says you might unwittingly carry a nuisance plant or animal out of the water and spread it. He says two of the most common invasive species are the zebra mussel and the Eurasian milfoil. The zebra mussel is a mussel or clam that has invaded from Europe and the milfoil is a plant that can grow very dense and impede boating, swimming and fishing. Martin says you should thoroughly clean off your boat when you take it out of the water. He says the milfoil is visible and you should look for plant material when you pull onto the boat ramp and remove it. He says the mussel isn’t always visible, so you have to take precautions. He says drain all the water out of the live well of your fishing boat and let it dry for four days so all the plant or animals die and you don’t infest another water body. Conrad says you should clean off everything after getting the boat out of the water — even you dog. He says the zebra mussel has a free swimming form called villager that could get onto the animal’s fur and be transported to another body of water. Conrad says some Iowa waters already have the nuisance species and they don’t want them to spread.He says the Mississippi River has both, and Crystal Lake in Hancock County and Snyder Bend in Woodbury County have infestations of Eurasian milfoil. Conrad says boaters who’re careful can prevent the spread of the mussel and milfoil to other waters.