I guess that would depend on the specific pond. Clipper deactivates rather quickly (especially with high PH) so it does not stay active in the system for more than a couple days at best. Clipper is not a cure all to fix the pond or the initial cause of the watermeal, but rather just is a tool to kill the watermeal that is present at that time.

I have successfully wiped out watermeal that has not returned on many lakes and ponds, but that is by killing it initially and then aerating and applying bacteria to reduce the nutrient load.