How do colonies of cyanobacteria harm aquatic organisms?

Question

How do colonies of cyanobacteria harm aquatic organisms?

Answer 1

The problem with cyanobacteria is that they can be harmful and in an alga bloom then can cover the surface cutting off any light to other plants and producing toxins that kill fish and other life forms.

"Certain cyanobacteria produce cyanotoxins like anatoxin-a, anatoxin-as, aplysiatoxin, cylindrospermopsin, domoic acid, microcystin LR, nodularin R (from Nodularia), or saxitoxin. Sometimes a mass-reproduction of cyanobacteria results in algal blooms."

They do provide nitrogen for other plant life.

According to Wikipedia:  http://en.wikipedia.org/wiki/Cyanobacter...

"Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria (Greek: κυανός (kyanós) = blue). They are a significant component of the marine nitrogen cycle and an important primary producer in many areas of the ocean, but are also found on land."

Few plants can extract nitrogen from the air and need to get it from the soil cyanobacteria, some types of beans and peanuts are among the few that can withdrawal nitrogen from the atmosphere.  On land they are known as nitrogen fixers.