I have done that. My city has a natural gas power plant which discharges it's wastewater into the river. Next to the main torrent of water the rocks form a dam to create a calm pool of water to sit in. <br>It is dangerous though. There is an open spot with nothing separating the raging wastewater from the pool. That spot is a no-go spot for obvious reasons but the rest of the pool is safe to be in.