Got some more information from a source from Texas. Yes, Texas, the place with all the COWS. Was too lazy and sleepy to properly dissect it so here it is , in mass.*yawn*
Excessive Phytoplankton
(1) The abundance of planktonic algae (very green water) in a pond is generally related to the amount of nutrients present in the water. Nutrients can wash into the pond from woods, pastures, fields, human activities in the watershed, or come from pond fertilization.
Generally, the more nutrients, the more planktonic algae (or other aquatic plants) will grow or bloom. Although phytoplankton is good from an abundance of natural food and oxygen producing standpoint, it can become too abundant or excessive.
When phytoplankton become so abundant that water visibility is limited to less than 12 inches there is a danger of an oxygen depletion. These heavy or dense blooms use large amounts of dissolved oxygen at night and on very cloudy/overcast, windless days causing an oxygen depletion and fish kill.
This problem is often a consequence of overfertilizing, overfeeding, or excessive nutrients from livestock, fields, or septic lines.
Phytoplankton Die-off
(2)Phytoplankton populations, or blooms, can grow rapidly, particularly on sunny days when the water is warm and nutrients are available. Alternatively, they can die-off quickly, especially in the spring and fall as water temperatures change rapidly with weather fronts. However, a bloom die-off can occur at any time of the year with little or no warning.
Typically during a bloom die-off, the color of the water will start to change. Leading up to a bloom die-off the pond water may have a "streaky" appearance. Streaks of brown or gray-black through the otherwise green water of the pond is an indication that the algae are starting to die.
As the die-off progresses, the whole pond will turn from green to gray, brown, or clear. The pond water will typically clear after a die-off as the dead algae settle to the bottom.
Plankton die-offs cause rapid oxygen depletions for two reasons:
1) the remaining dissolved oxygen is consumed by aerobic bacteria and fungi in the process of decaying the dead algae
2) few live phytoplankton remain to produce more oxygen. Secchi disks can be used to monitor bloom densities. Any bloom that reduces visibility in the pond to 12 inches or less may cause oxygen problems.
Source:http://aquaplant.tamu.edu/contents/dissolved_oxygen.htm
