small dams on the gaujakoiva 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 nationally ie all surface waters during the period to according to latvian statistics thanks to investments made in building and renovating wastewater collection and treatment infrastructure in estonia from to the pollution load has decreased for bod