The primary sources of surface water in Lake and Moody Counties are the Big Sioux River and its intermittent tributaries, and Lakes Herman, Madison, and Brant. Seasonal variations in streamflow and lake levels are directly related to seasonal variations in precipitation. Dissolved-solids concentration in water from streams and lakes increases as streamflow decreases and lake levels decline. Eight glacial aquifers and four bedrock aquifers were delineated in Lake and Moody Counties. The Big Sioux, North Skunk Creek, Pipestone Creek, Battle Creek, and East Fork Vermillion aquifers are composed of glacial outwash. These aquifers are less than 60 feet below land surface, and are in hydraulic connection with the river or creek of the same name. The Rutland, Ramona, and Howard aquifers are composed of glacial outwash and are overlain by 50 to 470 feet of till. The four bedrock aquifers are the Niobrara, Codell, Dakota, and Quartzite wash. The average thickness of the Big Sioux, Pipestone Creek, North Skunk Creek, Battle Creek, and East Fork Vermillion aquifers ranges from 14 feet for the Battle Creek aquifer to 39 feet for the North Skunk Creek aquifer. The average thickness of the Rutland, Ramona, and Howard aquifers ranges from 18 feet for the Ramona aquifer to 40 feet for the Howard aquifer. Predominant chemical constituents in water from the Big Sioux, North Skunk Creek, and Pipestone Creek aquifers are calcium and bicarbonate. Predominant chemical constituents in the Battle Creek and East Fork Vermillion aquifers are calcium and sulfate. Predominant chemical constituents in water from the Rutland, Ramona, and Howard aquifers are calcium, sulfate and biocarbonate. The average thickness of the four bedrock aquifers ranges from 60 to 400 feet. The aquifers are under artesian conditions. Predominant chemical constituents in water from the Niobrara aquifer are calcium, sodium, and sulfate; from the Codell and Dakota aquifers are sodium and sulfate; and from the Quartzite wash aquifer are calcium, sulfate, and bicarbonate. Water use in 1980 in Lake and Moody Counties was about 2.6 billion gallons. Ninety percent of the water used in the counties was withdrawn from the glacial aquifers and 10 percent was withdrawn from the bedrock aquifers. (USGS)