I had a farmer ask me, can he put plecos in his pond to deal with algae? It does not have hydro so a fountain is not really an option. Maybe someone has a better idea?
On a side note their usefullness as an algae eater is far out weighed by the amount of waste they produce. People always add them to aquariums as they misunderstand the breed...much like tangs . A common pleco can grow to over 12" long (some breeds up to 2 feet). The only one you should have in a home aquarium is a Bristlenose. Even a Bristlenose should be housed in no less then a 30gallong. Like most fish, they will grow to their aquarium size, but that is not good for the fish. Pleco's also create a ton of waste that they will not 'clean up' leading to even more ammonia and other issues. So no to the plecos, unless you are looking at doing water changes and gravel cleaning to the pond. I do not even suggest them in a regular aquarium.
I believe its actually illegal to release a fish into a waterway in Ontario (unless it was caught in the same waterway) without getting a permit first...
Ya the above poster is right, you can not release any fish into any waters. Believe it or not when I scoop minnows from the river I can't dump them back into the river, it has to at least 100 meters away from shore where their dumped.
I don't think it matters much in your typical man made backyard pond built with liner etc... But when I think of farm pond I envision 30-50 feet across I know a friend wanted to stock his with some kind of sport fish and the ministry wouldn't allow it.
All ponds need a source of water circulation... If he has no hydro to it, and its not fed by an underwater spring that may be a contributing factor.