Eutrophication, the gradual increase in the concentration of phosphorus, nitrogen, and other plant nutrients in an aging aquatic ecosystem such as a lake. The productivity or fertility of such an ecosystem increases as the amount of organic material that can be broken down into nutrients increases. This material enters the ecosystem primarily by runoff from land that carries debris and products of the reproduction and death of terrestrial organisms. Blooms, or great concentrations of algae and microscopic organisms, often develop on the surface, preventing the light penetration and oxygen absorption necessary for underwater life.

The Department of Water assesses the concentrations of nutrients in a variety of water bodies including river and estuary systems, stormwater drains and groundwater. Understanding the concentrations of nutrients both within and entering our rivers and estuaries will assist the department in assessing the health of waterways and in determining management solutions for impacts such as algal blooms and fish kill events.

The main cause of eutrophication in coastal waterways is nutrient overenrichment (nitrogen, phosphorus and silica). Other factors influence plant growth and the build-up of nutrient concentrations, and hence modify (or buffer) the response of a system to increased nutrient loads. These factors include hydrologic residence times, mixing characteristics, water temperature, light climate and grazing pressure.

This government website explains Everything you do in your backyard, your school playground, your farm or your business then has the potential to affect waterways lower down the catchment,and ultimately the ocean and marine life.

DECCW have developed a risk assessment tool to help identify and prioritise land use planning decisions that protect and preserve the health of estuaries in NSW. The tool is known as CERAT (Coastal Eutrophication Risk Assessment Tool) and can be used by non-technical experts.

CERAT consists of a water quality database, spatial information for an estuary and surrounding catchment, and a coupled series of catchment and estuary models for every estuary in NSW.

Richardson and colleagues reviewed literature linking jellyfish blooms with overfishing and eutrophication - high levels of nutrients.
Jellyfish are normally kept in check by fish, which eat small jellyfish and compete for jellyfish food such as zooplankton, he says.
But, with overfishing, jellyfish numbers are increasing. Jellyfish feed on fish eggs and larvae, further impacting on fish numbers.
To add insult to injury, nitrogen and phosphorous in run-off cause red phytoplankton blooms, which create low-oxygen dead zones where jellyfish survive, but fish can't.
"You can think of them like a protected area for jellyfish," says Richardson.

Eutrophication, or excessive nutrient enrichment, threatens water resources across the globe. We show that climate change–induced precipitation changes alone will substantially increase (19 ± 14%) riverine total nitrogen loading within the continental United States by the end of the century for the “business-as-usual” scenario. The impacts, driven by projected increases in both total and extreme precipitation, will be especially strong for the Northeast and the corn belt of the United States.

The article focuses on the rise in the level of phosphorus pollution in freshwater basins around the world. Topics discussed include eutrophication resulting from phosphorus pollution causing algal blooms, it leading to the mortality of water organisms due to lack of oxygen and light, and factors contributing to phosphorus pollution being fertilisers, sewage and industry wastes.

One of the most important types of water pollution, cultural eutrophication describes human-generated fertilization of water bodies. Cultural denotes human involvement, and eutrophication means truly nourished, from the Greek word eutrophic. Key pollutants contributing to cultural eutrophication include nitrates and phosphates, the main sources are treated sewage and runoff from farms and urban areas.