Azolla is a really valuable plant. It’s a rampant native waterweed, that is symbiotic with a nitrogen fixing bacteria, so, like legumes, it is capable of harvesting nitrogen out of the air and putting it into a form that plants can use as a fertilizer.
The dam is full of azolla – a little water weed that I encourage because it is symbiotic with a nitrogen fixing bacteria. Like legumes, it can grab nitrogen out of the air and stabilize it in a form that feeds soil and plants that are not so handily endowed with an in-built fertilizer factory.