A mat of cyanobacteria is found growing on a lake with dead fish floating along the edge. what has caused thes

Question

i dont understand this question.

=[

Answer 1

The lake is polluted.  The population of cyanobacteria has exploded and blocked the sunlight from getting into the lower reaches of the lake.  These organisms will die and decay.  As they are decaying they use up the available dissolved oxygen in the water.  The fish cannot breathe since the dissolved oxygen content has dropped below what can support the fish and other aquatic organisms.  They die and float upon the surface of the water.  They decay using up more of the dissolved oxygen compounding the problem.