Aeration

Aeration systems are designed to prevent stratification, a natural process in which lakes form 2 distinct water layers: an upper layer that is warm and has plenty of oxygen and a lower layer that is cold and has little if any oxygen.  The system consists of land-based air compressors that pipe air to diffuser stations on the bottom of the lake.  The movement of the bubbles through the water column brings the cold, un-oxygenated water to the surface where it mixes with the upper layer.

A de-stratified lake is much less likely to experience a catastrophic fish kill and is better able to grow fish (by expanding the area of oxygenated water where fish can live).  The introduction of oxygen to the depths also allows the decomposition of organic matter (muck) that has accumulated on the bottom over time. 

Fertilization

Just as you fertilize your lawn to make it more productive you can fertilize a lake.  The nutrients in the fertilizer promote the growth of phytoplankton (microscopic plants) which are the base of the food chain.  Phytoplankton are eaten by zooplankton (microscopic animals) that are in turn eaten by small fish which are then eaten by larger fish, etc.  Fertilization can increase the productivity of a lake by 3-4 times.  The darker water color that results from fertilization also decreases the depth sunlight can penetrate, thereby reducing the amount of aquatic weeds.