El Salvador's environment and natural resources ministry (Marn) has completed a study of 55 rivers, finding that in 2010 only 2% were in "good" condition.
Some 65% of the rivers sampled between April and July last year were found to be in "average" condition, meaning they restrict the development of aquatic life, Marn said in a release.
The remaining rivers were found to be in poor or terrible condition, the latter making the development of aquatic life impossible. None of the rivers tested were in excellent condition.
Most of the rivers sampled showed high concentrations of fecal coliform bacteria, which is related to the sanitation conditions in the surrounding areas, according to the release. The waters also show a high level of turbidity.
Water quality was worst downstream from populated areas and industrial or commercial zones and the level of pollution means that much of the water can no longer be used for irrigation.
Marn is working to strengthen water management through a national policy on water resources and an integrated water management strategy, the release said.