I have a 15'x10' natural swimming pool. We have a waterfall and uv filtration pump. Last season this algae covered the pool section, all the rocks, and the plant roots. It's green and when "living" had air bubbles all around it. Ive been manually scraping it off the rocks and vacuuming. There is still snow and ice on most of the pool. The plant section is open water. We won't turn the pump on until the frogs hav spawned. We don't have fish. The middle picture is a net filled with the stuff I've scraped off rocks. It coats the rock like a skin.

Hi @TuesdayChase and welcome to the NGA forums!
How long have you had the swimming pool? From you pictures, it looks like naturally forming algae which will (and should) occur on all underwater surfaces in any natural swimming pool or natural pond as it becomes established. The waterfall adds oxygen and the UV Light will help take care of the floating algae, but not surface growing algae. Actually, with the right amount of surface algae, the UV Light isn't really needed. Other than the algae you cleaned off the rocks, is the water clear? The algae produces oxygen, good bacteria that keep bad bacteria in check, and if your water is clear, it is doing it's job. If you are going to have a natural swimming pool, algae is part of the deal. In "regular" swimming pools, folks use all kinds of chemicals to kill off these beneficial micro organisms so they have "pristine" looking water and surfaces. Then they call the water "clean".

Hi Moon Shadows!
Thank you for the reply. We've had the pool for five years now. The first three years the plants kept it clear, only a bloom each spring but two years ago we got this fibrous algae/moss that spread like crazy and the whole pool was a murky swamp. We used a borrowed water pump to add more oxygen which cleared up the water, but last year we got this algae. The water was not clear, though maybe this algae was fighting off the other?

The added information helps. Since you have had the pool for 5 years, it is well-established and the Spring blooms are pretty normal. From your picture, I wasn't sure, but I thought it might be the typical green algae that clings to everything, but apparently it isn't. I wonder if you need to increase the aqua-garden area? Additional plants would take in more nutrients that are used by the algae. I am going to send you a PM with some info.