Cyanobacteria (blue-green algae) produce a plethora of toxins collectively known as cyanotoxins, these toxins include potent neurotoxins, hepatotoxins, cytotoxins, and endotoxins. they are usually cyclic peptides such as microcystins and nodularins or alkaloids such as Cylindrospermopsins, Saxitoxins and Anatoxin-a. Many cyanotoxids will bio-accumulate and will definately kill inversts and fish.
Inverts are used as "sentinal " organisms, when kick sampling is carried out we are looking for both abundance AND diversity... in terms of a river environment plecoptera are the most sensitive (stone and needle flies) then ephemoptera (upwing may flies), then trichoptera (caddis) finally gammarus (shrimp) (clearly this is a simplification) a healthy river environ will have good numbers of all species, as water quality declines the diversity of the sample population is reduced (not necessarily the abundance) the cause of these changes can be pollution or they can be a naturally occuring toxin such as a cyanotoxin
Blooms are most often attributed to hypertropication, the addition of nitrate and phosphate to a body of water, usually from fertilizer run off or sewage leaks. hypoxic conditions generally accompany an cyanobacteria bloom
