Children at the opening of Lincoln Park swimming pool in Seattle, 1925. This pool was dug out of dirt with a retaining wall of rocks along the sides. It filled with salt water from Puget Sound. A muddy bottom and control valves that did not always contain the water eventually required a pool made of concrete and tile. The Laurence Colman Pool, dedicated on July 4, 1941, is also filled with salt water from the Sound.