Water quality

Water quality is degraded directly through chemical or nutrient pollution, or indirectly when the capacity of ecosystems to filter water is degraded or when land-use changes increase soil erosion.

• Nutrient pollution from fertilizer-laden runoff is a serious problem in agricultural regions around the world; it has resulted in eutrophication and human health hazards in coastal regions, particularly in the Mediterranean, Black Sea, and northwestern Gulf of Mexico.

• The frequency of harmful algal blooms, linked to nutrient pollution, has increased significantly in the past two decades.

We have greatly overstepped the capacity of many freshwater and coastal ecosystems to maintain healthy water quality. And although developed countrieshave improved water quality to some extent within that same period, waterquality in developing countries – particularly near urban and industrial areas – has degraded substantially.

Declining water quality poses a particular threat to the poor who often lack ready access to potable water and are most subject to the diseases associated with polluted water.

Agroecosystems	Coastal ecosystems	Forest ecosystems	Freshwater ecosystems