Eutrophication is a process of increasing bio-mass generation in a water-body caused by increasing concentrations of plant nutrients, most commonly phosphorus compounds and nitrate, or other nitrogen compounds. Increasing nutrient concentrations leads to increasing fecundity of plants, both macrophytes and in the plankton. As more plant material becomes available as a food resource, there are matching increases in the number of herbivorous animals and also carnivorous animals feeding on them. As the process continues, the bio-mass of the water body increases but biological diversity decreases. In the more severe eutrophication the bacterial degradation of the excess biomass results in oxygen consumption, which can create a state of hypoxia throughout the water body. Hypoxic zones are commonly found in deep water lakes in the summer season due to stratification into the cold oxygen poor hypolimnion and the warm oxygen rich epilimnion. Strongly eutrophic freshwaters can become hypoxic throughout their depth following severe algal blooms or macrophyte overgrowths.