I just bought a property with a 1 acre lake. has a dirt and rock dam about 20+ feet high on the dry side maybe 75 feet across. the previous owner let the willows grow up in the dam along the waterline.. biggest is probably 8 to 10 inches across. I know they shouldn't be there but I don't know if I should just cut them down or wait till winter or poison them first or ????...you smarter people give me some guidance please...

All of the government agencies will advocate removal. If you poison them, they will have to be cut down sometime as they will rot and rot will follow the roots down.

If it were me, I would cut the larger ones off, about sitting high stumps, paint them with herbicide and enjoy a few years of fishing sitting on them. The other ones, cut off at ground level and use herbicide on them. Honestly for all the worrying the states do about them, and the loosening of soil, and trees blowing down in hurricanes, the only dams I have ever had have problems are beaver digging holes through them in dens and draining them,

Cut them all down and paint the stumps with Garlon. Pile them up let them dry and burn them

Our recommendations have have always been to stop any woody vegetation growing or encroaching on the face of and the downstream side of a man-made dam (permanent or temporary water storage). Kirk's advice was what I would recommend but you can use other herbicides to paint the stumps. 2,4-D and Glyphosate are both registered for cut stump treatments and are not restricted use herbicides (they are attainable at most farm stores)........................ the mike,,,,,,,,,,,,,retired civil eng. tech.