I've developed a bit of a habit, that I'm codifying into a Doctrine. At every embark, I use every single Stagnant Pool (those bits of water that are eerwhere on the surface). but not for fishing or anything like that. Nope, I use them for something better.
First step is to cut down all the trees near them. The more that fall into the pool, the better. Then, I dig out underneath the surface layer, and drain them completely. If some of the water goes over rocks, so much the better.
Next, I cover the pools with wood, making notes to be sure to replace the wood with Glass sometime in the future. These initial pools become less of an annoyance to mine around, and are first easy access to the surface to replace surface stockpiles with underground stockpiles, and then they become primary grazing land and a small handful becomes farming land. Since I tend to ebark with deep soil and sand, I'm starting to place my underground farms right next to the formerly stagnant pool surface farms, so I don't have to have separate food stockpiles, nor separate seed stockpiles, or potted seed feeder stockpiles.
Or the related workshops.
This replaces my former practices of channeling out surface areas, then sealing them off again--or finding areas with slight depressions that get walled off, roofed off, and turned into farms.
So now I ask you:
How do YOU exploit the Stagnant Pools, for the glory of the Sontaran Emp--er, Dorfen Empire!