I talked about this a little bit when Rob Tobeck was speaking at the last meeting I would hope he adds it to one of his shows. Here is some information you may find helpful about weed kills.
http://www.youtube.com/watch?v=hO1RhnQchdQ&feature=channel_page
http://www.watoxics.org/issues/pesticides-in-lakes/aquatics-problems
1 line that sticks out to me on the second link
for large lakes like Lake Washington, any property owner along the lake can apply for a permit to use herbicides in the lake without ever coordinating with or talking to their neighbors. There are no entities that coordinate vegetation management in Lake Washington, which led to upwards of 70 separate herbicide applications to the lake in 2004
I for one will not let my kid swim in the lakes after this stuff is applied.