Steve,
Your best bet would be to contact the DNR as they are the regulatory agency that would determine if Missouri clean water laws were being violated.
Kansas City Regional Office
500 NE Colbern Road
Lee's Summit, MO 64086-4710
816-622-7000
I spoke (email) with the DNR and explained the situation, they said it would be a civil matter between me and the developer of the subdivision and something they wouldn't get involved in. I'm guessing it would be difficult to find the developer as I'm sure they've long quit business. I've had DNR, MDC, State Representatives, City Engineer, etc, out here, nobody is interested or gives a flying...hence the reason for draining. however I spoke with the Corps of Engineers about a permit for breaching the dam, they said I didn't need one but I would be responsible for any silt, excessive runoff, wetland damage downstream. I was thinking, what about the people UPSTREAM from me, they've done it all !...what a crock. I made that point in my Email response to the Corps but naturally, never got anything back.