I've done some further searching on this subject. One thing I've found in a few places is a warning that even biodegradable soaps are harmful to fish. Something called "surfactants" present in even biodegrabable soaps and detergants.

excerpt from http://lists.saveourshores.org/pipermail/sos/2002-June/000002.html

All soaps and detergents even the biodegradable ones, are toxic to fish and
other aquatic life. The "surfactants" in most liquid detergents and
shampoos is called sodium lauryl sulfate which destroys the oxygen exchange
in the gills of fish. "Biodegradable" detergents still contain
surfactants. In their water quality testing procedures for safe release of
treated water or "effluent", the local sewage treatment plant, sewer
authority midcoastline, uses the harmful sodium lauryl sulfate as a
reference toxicant for our LD(Lethal Dose) 50 sensitivity check of their
bioassay fish. The dose at which 50% of the fish die ranges from about 17
PPM (PARTS PER MILLION) to 30 PPM.

I'm sure the volume of discharge and volume of water probably make a difference, but I guess I won't fool with it.