Diatoms live in all types of water and all latitudes and longitudes of the world. Diatoms are divided into marine and fresh water diatoms. Marine diatoms can be benthic(live on ocean floor) or planktic, which spend their lives, including their reproductive period suspended in the water column. There are also some neritic, which are afloat during their vegetative state, but their spores fall to the bottom where they wait through unfavorable conditions. The ability to float is essential for the existence of planktonic diatoms, and their structure has been modified for this function. In regions where there is substantial variation in water temperature from winter to summer, some species of diatoms have adopted winter and summer forms. The summer forms have a larger surface area to help them float in the warmer water, which is less dense.

There are several chemical and physical factors which affect the distribution of diatoms, these factors include the density, salinity, and temperature of the water. Water density is an important factor in the flotation of diatoms. The density of the water is affected by the temperature. Diatoms experience their best development at specific depths because the temperature, and therefore density of the water is enough to keep them afloat. Warm water diatoms are better developed at lower levels than cold water diatoms because of the difference in density.