Lake Whatcom is on track to drop to a low level not seen for nearly 20 years, largely due to evaporation and a lack of rain this summer.
The lake was at 312.2 feet on Aug. 16, down more than a foot from its July 1 level of 313.3 feet, said Eric Johnston, assistant director of Public Works.
To put that in perspective, a normal average low for October is 312 feet, which is also the level the city typically keeps the lake at in winter to control flooding on Whatcom Creek. Each spring, the level is usually raised to about 314.5 feet.
The levels are balanced as rainfall fills the reservoir, and a dam controls water flowing out of the lake.
But with the recent warm weather, city staff say the reservoir is losing water at about 4 inches per month solely due to evaporation, with little rainfall to replenish it. The city reports June and July saw only half to a third of the rainfall seen in previous years.
“We are definitely on track to see a low level that hasn’t been seen in some time,” Johnston wrote in an email to The Bellingham Herald.
If weather forecasts hold, the lake could drop a few more feet by the end of the year.
The lowest level in the last 20 years happened on Nov. 11, 1998, when the lake was at 309.8 feet.
Water usage by city residents, who get their drinking water from Lake Whatcom, has not played a major role in the water loss, according to the city.
“We’re not looking at water restrictions,” Johnston said. “Our customers do a great job of restricting water (use). ... The evaporation is by far the greater loss to that water.”
That said, the city does have a voluntary watering schedule through Sept. 15, that asks odd addresses water only on Wednesdays, Fridays or Sundays, and even addresses water only Tuesdays, Thursdays or Saturdays. Mondays are left as non-watering days to allow reservoirs to recharge.
For its part, the city will stop watering some of its lawns that get less use. Sports fields, play meadows and beaches still will be irrigated.
Those who own property on Lake Whatcom are advised to prepare their properties, docks and/or boats for the expected lower lake levels.
If the level drops below 310 feet, some private water intakes on the lake may no longer be submerged, meaning some residents could have problems getting water.
The lake could get down to about 308 feet before the intake for the city’s water treatment facility at Whatcom Falls Park might see changes in water flow, Johnston said. However, that water flow concern is based on the city using 20 million gallons per day.
“Bellingham consumers are so good at conservation that our peak demand periods on the hottest days ... this year were around 12 million gallons a day, with averages around 10 million gallons,” Johnston wrote in an email. “The low consumption means we have capacity and volume in the lake to meet demand.”
Aside from continuing to conserve water, there isn’t much else the city or users can do to prevent the level from dropping, Johnston said.
“If our water source were a swimming pool, we would simply cover it in response to the sustained warm temperatures and minimal rainfall,” Johnston said in a prepared statement. “But obviously this is not an option, and evaporation of the lake is inevitable when it is 10 miles long and 5,000 acres.”
According to the recent measurements, the lake is about two months ahead of its normal schedule, a trend city staff noted earlier this summer.