I have a ditch behind my house which collects standing water (the city
doesn't seem to want to solve the problem) and a HUGE mosquito problem.  I
also have a number of feral cats, raccoons, skunks, possums, etc. in the
area that I do not wish to harm with chemicals.  

Has anyone had experience with mosquito dunks?  They claim to be safe and
biologically sound, but I would appreciate some advice from first hand
experience to be certain.  I suspect that these animals drink water from
the ditch and I wouldn't want to do anything to cause illness.  On the
other hand, the mosquitos could very well be causing illness, so if the
dunks are safe it might be a good solution.  

Thanks,
Shelly