Puget Sound Off: Why Lake Washington water levels change

Why it matters: The lake's changing levels — which actually vary only by two feet a year — are fine-tuned to protect the ecosystem and support navigation, salmon migration, tribal fishing rights and dock maintenance, according to the corps.

How it works: The Hiram M. Chittenden Locks and Dams are used to control the water level of Salmon Bay, Lake Union, Lake Washington Ship Canal and Lake Washington, Shelia Fourman, a spokesperson for the corps Seattle district, told Axios in an email.

• A minimum elevation of 20 feet, as measured at the locks, is maintained during the winter months to minimize wave and erosion damage during winter storms, she said.
• It also provides storage space for heavy rains and allows for annual maintenance on docks and seawalls.

• The water stored between 20 and 22 feet helps supplement Lake Washington Ship Canal inflows during the summer/fall drawdown period, supporting lock operations, salinity drains, smolt flumes and the fish ladder facility.

By the numbers: The lowest recorded lake level was 18.34 feet in 1958, per Fourman, while the lowest since 2000 was 19.93 feet in 2015.

The intrigue: Lake levels are not flat across the lake, said Fourman. For example, lake elevation at Kenmore is typically .25 feet higher than at the locks due to wind and water movement.