some folks use rotenone but you need a special license to possess/dispense it or hire someone to do it for you. This likely would be a high cost.

From previous posts it seems that the most common way is to use hydrated lime which will quickly increase the PH level to where nothing can survive. Do a google search for something like "pondboss hydrated lime" and you should find a few threads where it is discussed.

1 ac pond LMB, BG, RES, CC