The U.S. Geological Survey conducted a water-quality study of the St. Croix National Scenic Riverway. This report documents the water quality during the period 1975-83. The water quality is good for most uses and is a calcium bicarbonate type. Concentrations of most constituents analyzed were less than most sites in Wisconsin. Constituent loads and yields were alsg lower in the Sceiilc Riverway than in other Wisconsin streams. Water-quality samples were collected at 10 stations throughout the study area and were compared to analyses of samples from selected National Stream Quality Accounting Network stations (NASQAN) and the Hydrologic Bench-Mark NetWork (HBMN) station in Wisconsin.

The average suspended-sediment concentration for 9 of the 10 stations in this study was 7.7 milligrams per liter. This compared with an average suspended-sediment concentration of 11 milligrams per liter for two other stations in the scenic riverway and an average suspended-sediment concentration of 110 milligrams per liter for Wisconsin. Concentrations of major cations and anions were generally below concentrations at other stations in the State. The concentrations of major cations and anions at two of the stations were similar to concentrations at the HBMN station Popple River near Fence. Mean total phosphorus concentrations ranged from 0. 02 to 0. 08 milligram per liter at the study stations and from 0.03 to 0.16 milligram per liter at selected NASQAN stations. Concentrations of trace metals were below safe drinking water standards at all the study sites except for iron and manganese which exceeded drinking water standards at some of the study sites. Pesticides were sampled at the St. Croix River at St. Croix Falls and above and below cranberry bogs that drain into the Namekagon River. No pesticides were detected in the water/suspended-sediment mixture or bottom material.

Average annual loads of suspended sediment, total phosphorus, total nitrogen, and dissolved solids were calculated by a flow-duration curve method. Annual suspended-sediment loads ranged from 580 to 25,000 tons per year at the study stations. Annual suspended-sediment loads at the HBMN station and NASQAN stations ranged from 720 tons at the Popple River near Fence to 443,000 tons at the Chippewa River near Durand. Average annual total phosphorus loads ranged from 6,800 to 900,000 pounds at the study stations compared with 145,000 to 1 ,600,000 pounds at selected Wisconsin NASQAN stations.

Yields for suspended sediment, total phosphorus, total nitrogen, and dissolved solids at the study stations were consistently lower than at other stations in the State. Suspendedsediment yields ranged from 1.9 to 13.3 tons per square mile. The average suspended-sediment yield for Wisconsin is 80 tons per square mile. Total phosphorous and the other constituents exhibited the same trend.