One of the parameters that we measured was dissolved oxygen. Dissolved oxygen concentration in a lake is a measurement of the amount of gaseous oxygen dissolved in the water. Because organisms rely on this oxygen for respiration, water with a DO concentration of less than 5 ppm is considered dangerous for cold water fish. When levels fall below this, fish kill like the one in the picture may occur. When DO concentration falls below 1 ppm, the water is termed anoxic. DO levels are affected by many factors, including decomposition, microbial activity, respiration, turbulence, wind disruption, salinity, and temperature.