The filtration system of our backyard pond failed at some point last winter and the pond had become quite alga-filled. Jim spent the morning catching koi, transferring them to a holding pool, and draining and cleaning the pond -- discovered the shop vac worked well to remove all the leaves and muck from the bottom and sides of the pond. Yay! He then set up a new, larger pump and filter and refilled the pond with water. The fish were a little skittish in their clean home but were loving the waterfall.