Cecil, I have crayfish too that I am pretty sure are compromising the bottom. If you find a hole in a spot that is subject to cause failure, I would heed the advice given. Now days, pesticides are very low dosage and slow acting nerve agents for insects. They are made so that insect colonies can pass it around before it does its duty. Boiling water would work, just as it works on ants. Gasoline would also.
You could always go the dydamite route, but that could also compromise the dike. I got that idea from Tom G., nevermind.
