Watershed and Lake Facts
The Lake Whatcom watershed covers an area of about 56 square miles (36,000 acres). That total includes the surface of Lake Whatcom, which is about 4,994 acres. It boundaries are defined by five major surrounding peaks: Squalicum Mountain (1585 ft) to the north of the lake, Stewart Mountain (3080 ft) to the northeast, Anderson Mountain (3364 ft) to the southeast, Lookout Mountain (2677 ft) south of Sudden Valley, and Galbraith Mountain (1745 ft) southwest of Sudden Valley.
In all, 23 subwatersheds comprise the Lake Whatcom watershed. There are approximately 36 creeks and tributaries that flow into Lake Whatcom. The primary perennial flows into the lake are from Austin, Smith, and Anderson Creeks. Perennial creeks are those that have flowing water year-round. Additional creeks in the watershed include Fir, Brannian, Silver Beach, Carpenter, Olsen, and numerous no-name creeks. These creeks are smaller and can be seasonal, drying up during the warm summer months, depending on the year.
In addition to the numerous creeks draining directly into Lake Whatcom, flows into the lake are supplemented by water diverted from the Middle Fork of the Nooksack River. The Middle Fork diversion discharges into Mirror Lake, for which Anderson Creek is the outlet.
Lake Whatcom drains naturally into Bellingham Bay via Whatcom Creek. Areas where fresh water mixes with saltwater are called estuaries. You can visit the Whatcom Creek estuary at Maritime Heritage Park in downtown Bellingham.
Lake Shape (Bathymetry)
Lake Whatcom is nearly 12 miles long and just over a mile wide at its widest point. Its average elevation is 314 feet above sea level. It has approximately 30 miles of shoreline and holds about 250 billion gallons. It is typically described as having three basins. Each of the basins is distinquished from the other by what is called a sill (a shallow underwater ridge).
The first basin, Basin 1, extends from the lake’s outflow at Whatcom Creek near Bloedel-Donovan Park to the Geneva Sill at about the end of Austin and Fairview Streets. The maximum depth in Basin 1 is about 95 feet, with an average depth of 30 feet.
Basin 2 extends from the Geneva Sill to Strawberry Sill at Strawberry Point. The maximum depth in Basin 2 is about 69 feet, with an average depth of 38 feet. The water intake for the City of Bellingham municipal water supply is located in Basin 2 at a depth of 35 feet. The total volume of water in Basin 1 and 2 is about 4% of the total volume of water in Lake Whatcom.
Basin 3, which contains about 96% of the total volume of water in Lake Whatcom and receives more precipitation than Basins 1 and 2, includes the entire southern portion of the lake starting at the Strawberry Point sill. The maximum depth measured in Basin 3 is 328 feet (99.97 meters) and averages 178 feet. The water intake for the Lake Whatcom Water and Sewer District’s Sudden Valley customers is located in Basin 3 at a depth of about 70 to 75 feet.
To view a map showing the three basins and their longitudinal profile go to the following website: http://www.cob.org/gis/maps/lake-whatcom.htm
Other Facts
Climate - The mean annual temperature at lake level is 50 degrees F with 150 - 190 frost-free days each year. Precipitation varies considerably depending on the location in the watershed. The north end of the watershed receives about 45 inches per year with the south end receiveing 60 inches annually. Most of this rain falls between October and May. Each summer month averages only about one inch of rain.
Lake Stratification - Lake Whatcom, like many deep lakes in the northwest, forms layers (stratifies) because the density, or weight, of the water changes as its temperature changes. In the summer, stratification occurs when the sun combined with wind action and water currents begins warming the top layer of the lake. This upper layer, the epilimnion, is characterized by warmer, less dense water. It is in this layer that the greatest amount of biological activity occurs. The bottom layer, which is called the hypolimnion, has colder water.
The middle layer, the metalimnion, is a narrow band between the epilimnion and the hypolimnion. Water in the metalimnion is colder than the epilimnion and warmer than the hypolimnion, which helps to prevent mixing between the upper and lower layers. This middle layer contains the thermocline, which is the area where a rapid change in temperature occurs.
In the fall, the surface of the lake cools decreasing the temperature difference between the epilimnion and hypolimnion. As the thermocline begins eroding, the lake is said to “turn over” resulting in a more complete mixing of the lake.