Washington State’s historic drought is pushing Lake Washington and Lake Union below the normal annual 20-foot mark for the first time in 28 years, and officials anticipate another foot drop.

Lake levels typically hit the 20-foot mark in December, according to U.S. Army Corps of Engineers Senior Water Manager Ken Brettmann. The measurement went below 20 feet, officially measured at the Hiram M. Chittenden Locks in Ballard, around 9 a.m., Aug. 25. The lowest recent recorded level below 20 feet is 19.44 feet, measured in late October 1987.

The Corps usually begins raising lake levels in February, reaching 22 feet by late May or June. The higher level helps meet water use between June and October when inflows are generally low, providing water necessary for fish passage, navigation and salinity control. Water is slowly consumed throughout the summer, until it reaches the winter level typically in early December.

This year, early concerns prompted Corps officials to speed up the annual refill reaching a 21.95 foot elevation in early May.

“The low snow pack and early forecasts prompted us to accelerate the annual refill compared to normal years, and we also started water conservation efforts in April, which is unprecedented,” Brettmann said. “Based on weather predictions, forecast inflows, and expected evaporation we anticipate the minimum lake level this year to be about 19 feet, about another foot down from where we currently are.”

Because any of the factors can change and could potentially affect the lake level, Brettmann and Corps officials are urging everyone to prepare for a minimum as low as 18.5 feet. Early conservation measures the Corps implemented, limiting smolt flume usage for juvenile salmon and maximizing lockage efficiency, has so far saved an equivalent of nearly a foot of lake level. Without those conservation measures, the minimum projected lake level would be 18 feet, below the current record low 18.35 foot level recorded in 1958.

“The locks staff has done an excellent job of efficiently using the locks to move vessels and save water,” said Brettmann, who oversees reservoir regulation at all Corps Western Washington projects. “Recreational boaters are waiting up to an hour, perhaps a little longer, depending on vessel traffic. We understand the hardship for many associated with the lake dropping below the 20 foot mark, but this is an extreme year.”

Brettmann added it’s unlikely that next year will be this extreme, but it’s important people be prepared and understand these events happen, so be prepared.