I am not an expert on this chemical, but have read it is extremely toxic to multiple types of life forms, including human.  In 1983, I was involved in monitoring effects of aerial application of carbaryl, also a carbamate.  These are of the same general chemical family of pesticides, but likely very different in toxicity.  Sevin (carbaryl) is a fairly common chemical used in dilute form in gardens, on pets, etc. But the report of its use and spills suggests fast mortality when sprayed over streams or for spills into streams like Willow Creek.  Some organisms are able to come back, others will take time and perhaps not.  From what I have read, carbofuron is much more toxic to everything, and if individuals are applying it to kill pests, who is to know how much they are using and what is the toll on non-target life forms or is chemical moving out and being dispersed during inundation fluctuations common to some hydropower operations.  Under some conditions, I have learned that chemicals break down in aerobic conditions but not in anaerobic conditions (ie, wetlands).  I don't know relative to carbofuron how it breaks up and whether being in a wetland affects it.  Some things as they breakdown, have even more toxic forms.  I am attaching that large report that is on my researchgate site and it was written when I was moving from Oregon to South Carolina, so I did not have enough time to improve.. Just to be clear, I have no direct knowledge about the uses of carbfuron you are analyzing or its toxicity. But the information I have in the 1983 report might be of use.  Basically things die if the carbaryl-diesel mix we used was applied aerially at specified rates and streams were not adequately buffered or the full batchtruck mix spilled into waters effectively killed everything for miles.  If the use is to kill organisms for food for people or animals, that may also have toxic or health effects.