From Homestar Runner Wiki
The Pond is a foggy lake where Strong Bad and Coach Z go fishing in the email lures & jigs. It is stocked with fish and makes a suitable location for a romantic date with a Wagon Fulla Pancakes in montage. A few ducks live there too, seen in the email/game duck pond.
In Baddest of the Bands Strong Bad refers to it as "The Ol' Fishin' Hole" and claims that it's got more apostrophes in it than fish. However, after the pond is bleached, some dead fish float to the surface, proving that it isn't (well, wasn't) nearly empty after all.
In several toons, it has been shown frozen over.