Pond Boss Forums AQUATIC VEGETATION Controlling unwanted plants Blue dye pros and cons

It quite possibly could be nutrients in the inflow, but if your inflow is a true spring I find it unlikely. Just be careful about jumping to the conclusion that you are recieving too much N and P. There are lots of issues besides N and P that facilitate fillamentous algae blooms. Just another side of things.
I am curious though, do you have plankton blooms with the fillamentous algae, or just the fillamentous?
Another thing to think about, if your spring is constantly causing your pond to overflow the only way you could have too much N and P in the pond is if the spring consistantly has high concentrations. I do agree that if you are worried about a septic tank seaping into your pond the fecal colliforms would be a good test.