A body of water naturally goes through an ageing process called eutrophication.
This process, which takes many years, eventually causes the water body to fill with sediment and vegetation. It then progresses from open water to swamp, marsh and eventually to bush-land.

However , As more people live and grow crops near the shores of our lakes and rivers, cultural eutrophication ( premature ageing of the water body ) can occur.
To differentiate between natural and developmental impact, comprehensive studies need to be conducted to assess the nutrient and hydrologic budgets of the water body.

Excessive nutrient levels are damaging to a natural water body because this provides extra food for the algae and aquatic weeds which are naturally present.
This extra plant biomass can become very dense and cause stunting or even death of other organisms such as fish.
It can also reduce the commercial and recreational uses of the water body.

The best way to solve this problem is through total nutrient reduction within the catchment/watershed and this should be the ultimate aim of any environmental solution, However this is a long term technique and must be coupled initially with some immediate action to reduce the growth and accumulation of biomass already present in the environment.