What Should We Do?

Yesterday afternoon, around 3PM, I was making my way home down Barry in a moderate rain.  From the top of Barry east of East Side down the hill a steady stream of chocolate water made its way downhill...towards the lake.  I decided to turn on to Hillside instead of my usual Potomac.  As I turned on to Hillside there was a steady stream of dark brown water, evading silt fences and going into the stream...that leads into the lake.  The water was going across a City street, into the creek that led into WLIC property...our lake.  We are about to embark on a very expensive dredging operation, a big piece is North Cove.  The City has laws that could be enforced, WLIC has gathered (I am told) lots of data regarding the situation (Stream Team).  So in answer to ANON's question, I will pose a question...If your neighbor continues to do an activity that harms your property, despite their promises and talking nice...what would you do?