How do I get rid of rivers otters?

We have a floating house (build on styrofoam) on a lake and a family of otters have moved in under us on the foam. They leave droppings all over the walkway and boat slip and leave dead fish on the styrofoam where we can't get to it. It is very stinky! They are chewing on the wood under the house and chewed through the water line. We tried trapping them on the bank but they didn't take the bait (dead fish, cat food). We tried critter ridder and put up a sonic pest repeller but that didn't work either. We would like to be humane in their removal but are getting to the point that any removal is needed. Any ideas?