Mill Creek overflowed into Walla Walla and College Place on March 31, 1931, causing $1 million in damages. Community volunteers jury-rigged makeshift levees to divert water from buildings during the cleanup which cost roughly $100,000. The United States Army Corps of Engineers built the Mill Creek Dam and Bennington Lake in response to the disaster. The dam and lake were instrumental in preventing damage from flooding in 1964, 1996, and 2020.- Walla Walla, Washington (Wikipedia)
Walla Walla is a city in Walla Walla County, Washington, where it is the largest city and county seat. It had a population of 34,060 at the 2020 census, estimated to have decreased to 33,927 as of 2021. The population of the city and its two suburbs, the town of College Place and unincorporated Walla Walla East, is about 45,000.