Ponds, simply due to their structure of being a big depression in the ground, are catch-all’s for a lot of things. Unfortunately a lot of this accumulation is organic debris that will eventually break down into a messy muck or sludge.
It’s been said that one of the pond owner’s main goals, if not THE main goal is to slow this process of “filling in” down as much as possible. Once this muck starts to rot and stink, it’s built up to the point where the pond’s natural assimilation processes just aren’t able to keep up with it any longer.
What’s unfortunate is that this mucky compost doesn’t just affect the bottom of the pond. And while it’s true that it serves as a really easy place for weed seeds to get established and rooted, it also releases so many nutrients that algae will often form below and above the water’s surface.