The researchers studied pollution in the Haihe River basin in 2005 by analyzing water and sediment samples from 4 river mouths. They found that the water at these river mouths is seriously polluted, with mercury being the major heavy metal pollutant. Two river mouths are also seriously eutrophicated. However, the concentration of heavy metals has significantly reduced since 2001, and water quality has improved at two river mouths. The sediments are not heavily polluted by heavy metals but are polluted by nitrogen and phosphorus, although less than in 2001. This suggests that recent pollution control measures have been effective, but there is a need to monitor water eutrophication in areas far from cities.