Holomictic references the most common type of lake which turns over at least once per year (as opposed to meromictic lakes which are constantly stratified). This mixing is an important process for maintaining fish and aquatic communities by distributing nutrients and oxygen throughout the lake before stratification occurs again. There are four categories of holomictic lakes:
- Oligomictic: mixing is irregular,
- Monomictic: turnover occurs once a year (most common in polar areas)
- Dimictic: turnover occurs twice a year (most common in temperate areas), and
- Polymictic: frequent turnover (most common in tropical areas).