Historic Record Flood level at Clinton, Iowa - River Gauges on Waymarking.com

In the spring of 1965, a very fast warm-up combined with heavy snow blankets in areas to the North created a fast snow melt that drained to the Mississippi River. Rains in the area added to the flow. Much of the lower areas of Clinton were flooded, including the downtown. A heroic effort by the local National Guard prevented the towns only drinking water supply, a well, from being contaminated and it's pump motors from being destroyed. They built a 12 ft dike of sandbags and plastic sheeting around the well structure and manned it 24 hr/day while surrounded by the rageing river. It became known as Fort Johansen, named after the Lieutenant who was in charge. On April 28, 1965 the river finally crested and started to slowly drop.

Since that flood, a dike has been built to protect the city of Clinton. Several other years since then have seen some major floods, but none have reached the high water mark of 1965.