I agree it is a good idea and use of goats.
Some City planners have already been doing this on detention ponds for about a decade.  It isn't cheap to rent goats.  It is cheaper to mow ponds with equipment if you can get it in.  Of course this works best on ponds that are already fenced.  I like this idea but would only use it on ponds with access issues or which are hard to mow (steep slopes, uneven ground or some other constraint).  Hey everyone have a great day!