When algae die, they are decomposed by bacteria, which can remove oxygen from the water, occasionally killing fish. Algal blooms can also make water unfit for even recreational use. These tiny organisms can therefore have a huge impact on health, wildlife and economies that depend on fishing and tourism
Are there signs that an algae dies?
After the algae cells die, they begin to lose their chlorophyll and green coloration. This is why a tell-tale sign of a die-off is a change in water color, in streaks or entirely, from green to brick-red, brown, or black, and can give off a foul odor.
This is because they give oxygen to the water?
Yes that is why it says, oxygen can be removed.