What are some bad/horrible things that grow in the water in any water environment (lakes, rivers, ponds etc.)?

Question

What bad things grow in water and how this happens like moss and other things.

Answer 1

there are many water born diseases

http://www.lenntech.com/Waterborne-disea...

Answer 2

Have you ever heard of harmful algae blooms?

Harmful algal blooms may cause harm through the production of toxins or by their accumulated biomass, which can affect co-occurring organisms and alter food-web dynamics. Impacts include human illness and mortality following consumption of or indirect exposure to HAB toxins, substantial economic losses to coastal communities and commercial fisheries, and HAB-associated fish, bird and mammal mortalities.  To the human eye, blooms can appear greenish, brown, and even reddish- orange depending upon the algal species, the aquatic ecosystem, and the concentration of the organisms.  These outbreaks are commonly called red tides, but scientists prefer the term "harmful algal blooms" (or HABs).

What causes these blooms:

Blooms can be caused by several factors. An increase in nutrients can cause algae growth and reproduction to increase dramatically into a bloom just as fertilizing a lawn makes the grass grow faster. In other instances, something may change in the environment so that certain algae can out compete the other algae for food, which can result in a bloom of the algae with the advantage. This environmental change can be related to the water quality, temperature, nutrients, sunlight, or other factors.

How are HABs dangerous to fish and humans?

HABs are dangerous to fish because they can deplete oxygen in water. When oxygen levels become too low, fish suffocate and die. Some algae species in blooms produce toxins that can kill fish and cause illness in humans.

Cyanobacteria are also bacteria that grows in water environments.  They live in environments that dont have any oxygen but produce oxygen.  They are often found in marshes etc.  It is thought that Cyanobacteria were the first living organism on the earth and that it was this bacteria that lead to the evolution of the oxygen rich atmosphere that supports life today

Answer 3

some horrible african people grew out of the water environment at New Orleans...

Answer 4

There are invasives, such as purple loosestrife; disease-causing agents, such as Cryptosporidium; dangerous fishes, such as Urinophilus ....

Answer 5

Water Hyacinth is a plague in some rivers. It grows fast and blocks waterways, snags propellers etc.

There are lots of water-borne diseases everywhere

Answer 6

Nessie