Are Pond Algae Edible for Humans?
I came across a this Wikipedia page which said blue green algae from ponds can be used as dietary supplement (in tablet form).

Many other articles on the internet like  here suggest it is included in many diets in many places across the globe. 

However, without proper regulation one can include a heavy metal contaminated vegetable to their diet which is detrimental to health. Furthermore cyanobacteria are known to produce toxic substances known as microcystins which can cause damage to human organs as well.

So unless you are certain of the biochemical balance of your pond I would  recommend not integrating it in your diet. Rather you can find commercially available ones which your local regulatory authority(s) recommend for dietary purposes.