Small dams on the Gauja/Koiva’s tributaries which no longer have a water management function, have an adverse effect on the fish fauna. River fragmentation by dams on the Parlijogi and Vaidava rivers, resulting in problems for fish migration, cause these rivers to be of moderate status. This has contributed to the reduction of pollution load to surface waters, which for phosphorus, nitrogen, BOD, COD and suspended solids has decreased by 10-40% nationally (i.e. all surface waters) during the period 2004 to 2008, according to Latvian statistics. Thanks to investments made in building and renovating wastewater collection and treatment infrastructure in Estonia, from 1992 to 2007 the pollution load has decreased for BOD.