The Rumsey Gauge
"What is Zero Rumsey?"
The natural level of Clear Lake is maintained by the Grigsby Riffle, which is a rock sill located at the confluence of Cache and Seigler Creeks near Lower Lake. The natural low water level of Clear Lake was established as "Zero Rumsey" and all subsequent lake measurements are based on this elevation.
As a legal measure, the Gopcevic Decree of 1920 establishes Zero Rumsey as 20.01 feet below the center of the large concrete star at the northeast corner of court house yard in Lakeport. Zero Rumsey is equivalent to 1318.25 feet above sea level (1929 NGVD) and full lake is established as 7.56 feet on the Rumsey gage. In 2014, after several years of drought Clear Lake dropped to -.75 Rumsey, and water no longer flowed out of the lake. A few laters in 2017, Clear Lake rose to 10.6 Rumsey, its highest level in nearly 20 years.