One of the most common sources of phosphate pollution that has led to eutrophication has resulted from the use of

Phosphate fertilizers

Explanation:

One of the most common sources of phosphate pollution is run-offs from phosphate fertilizer from agricultural processes. Farmers deploy phosphate-containing fertilizers to soils in other to improve the overall fertility of the soil and the yield of crops.

Some of these fertilizers find their ways into nearby water bodies through washing up by erosion thereby raising the phosphate levels of these water causing eutrophication.

Other common sources of phosphate pollution include industrial and domestic run-off as well as detergents although phosphate-containing detergents are now becoming a thing of the past.