Lakes

Small lakes - water quality in small lakes

About this indicator: DNRP's goal is to maintain all beneficial uses of county lakes. In this region, high concentrations of the nutrient phosphorus are often correlated with increased algal growth. Thus, if the amount of phosphorus entering lakes is controlled or reduced, algal blooms are likely to decrease. Algal blooms are a nuisance because they can cause scum to form on the lake's surface and occasionally give a foul odor and taste to the water. When a bloom dies off it can also deplete the oxygen levels available to other aquatic life. In rare circumstances, algal blooms can become toxic.

Phosphorus concentrations in lake water as an indicator assess the potential for nuisance or toxic algal blooms that impact lakes, facilitating allocation of limited county resources toward restoring lakes with indications of serious degradation. This indicator uses summer phosphorus concentrations converted to Trophic State Indicators (TSI-TP) to assess conditions. Trophic State Indicators relate phosphorus to the amount of algae that the lake can support. Values below 50 have low or moderate potential for nuisance algae blooms; values above 50 have a higher potential.

Status: King County monitored 42 lakes in 2006, 16 of which were funded by city contracts. Slightly more than 80 percent of the lakes have good water quality with low potential for nuisance algal blooms.

Influencing factors: Lake water quality varies annually and is affected by many factors depending on the conditions in each lake. Phosphorus can be managed through drainage system design, increasing sewer service, and encouraging homeowners through education and incentives to use best management practices. Although large amounts of algae may relate to changes in conditions, this increased presence may not always reduce beneficial uses. However, a trend in a particular lake toward increased TSI-TP over time is probably due to changes in the watershed and cannot be discounted.

Existing DNRP response: We continue to monitor the managed lakes and implement elements of the Lake Management Plans under county jurisdiction, with community support, as funds become available.

Priority new actions: Lake management plans will be considered if any other county lakes begin to show serious deterioration in terms of beneficial uses. Monitoring data will be available online beginning in mid-2007.

---

Large lakes - fecal bacteria at swimming beaches in large lakes

About this indicator: When fecal coliform bacteria are found in lake waters it indicates that the water has been contaminated with fecal material from humans, birds or other animals. Although fecal coliform bacteria themselves are usually not harmful, they often occur with other disease-causing bacteria so their presence indicates the potential for pathogens to be present that are a risk to human health.

Status: Bacterial counts at all swimming beaches monitored in lakes Washington, Sammamish and Green Lake in 2006 were within acceptable ranges and did not warrant swimming beach closures. Bacteria levels were low in Green Lake for the second year in a row, while Lake Washington and Lake Sammamish remained fairly consistent, with slight variability from year to year. The 2007 target and long-term outcome for swimming beaches on large lakes is that none of the testing sites violate the fecal coliform bacteria target of 200 colonies per 100ml of water.

Influencing factors: Fecal coliform bacteria can enter lakes from household pets or farm animals, wildlife, stormwater runoff, untreated wastewater effluent, sewage overflows or failing septic systems. The most impacted beaches are adjacent to streams draining urbanized watersheds.

Existing DNRP response: King County routinely monitors swimming beaches during the summer months to determine levels of bacterial pollution and works with Public Health - Seattle & King County to estimate relative human health risks. If bacterial counts at swimming beach testing sites are greater than 200 colonies per 100 ml of water, the beach will be temporarily closed. By matching the bacteria genetically to its source, King County scientists have identified waterfowl as the primary source of the fecal coliform contamination at many of the beaches during these times.

Priority new actions: Changes to park maintenance procedures and control of non-migratory, non-native waterfowl should reduce bacteria counts and improve the water quality at large lake swimming beaches. Efforts to identify and correct bacterial source in the urban streams that discharge adjacent to swimming beaches has begun. A Total Maximum Daily Load (TMDL) for bacteria in Thornton Creek has been started.

---

Large lakes - fecal bacteria at non-swimming beaches (ambient) in large lakes

About this indicator: The presence of fecal bacteria in waterbodies indicates contamination with the fecal material of humans, birds or other animals. Fecal coliform bacteria can come from household or farm animals, wildlife, stormwater runoff, untreated wastewater effluent and failing septic systems.

Although these bacteria are usually not harmful, they often occur with other disease-causing pathogens, so their presence at high levels indicates an increased possibility that people might get sick if they come into contact with the water.

The lake standard for fecal coliform bacteria addresses human safety due to direct contact with the water from activities such as swimming and wading. The standard is a geometric mean value of less than 50 colonies/100 ml and not more than 10 percent of all samples obtained for calculating the geometric mean value shall exceed 100-colonies/ 100 ml. Sites used for this indicator are located in both mid-lake (open water) and nearshore locations in King County's three largest lakes — Washington, Sammamish and Union. This environmental indicator is based on data collected at the routine monitoring sites and does not include sampling done in conjunction with emergency overflow events.

Status:Even though this measure uses a standard that is exceptionally difficult to attain, 100 percent of the Lake Sammamish stations, 92 percent of Lake Washington stations, and 80 percent of Lake Union stations have achieved the lake standard for fecal coliform bacteria. Lake Washington showed a decrease from 2005 of 8 percent, due to higher bacteria at one station (4903).

Influencing factors: Roughly half of the samples that had higher fecal coliform levels were the result of unusual storm conditions with the highest bacteria concentrations collected directly after record rainfall swept through the region in November 2006. Lower percentages in Lake Union are attributed to the influence of combined sewer overflow and stormwater outfalls into the lake.

Existing DNRP response: DNRP will continue its extensive monitoring efforts to detect potential and existing problems with the stormwater and wastewater treatment system. In addition, King County's Combined Sewer Overflow (CSO) program is employing various ways to control CSO's including controlling pollution at its sources, optimizing flow management, monitoring and modeling flows in the system and constructing CSO control facilities.

Priority new actions: King County expects to build about 20 Combined Sewage Overflow control projects during the next 30 years.

---

Large lakes - water quality (phosphorus) in large lakes

About this measure: The people of King County have made significant investments in water quality improvement and protection to lakes Washington, Sammamish and Union beginning with the diversion of wastewater effluent out of Lake Washington and Lake Sammamish in 1968.

Improvements have continued with efforts to reduce the amount of stormwater discharges through combined sewer overflows, expected improvements in King County's wastewater treatment system from construction of the new Brightwater treatment facility and expansion of effluent reuse programs. These gains in water quality are constantly threatened by increasing amounts of phosphorus entering the watersheds as a result of increased development.

Status: Lake water quality results vary annually, depending on the weather and other biological interactions that combine to create unique conditions in each lake. For example, the 1994-2006 results for Lakes Sammamish and Washington show values fluctuated between the low to moderate threshold from year to year, indicating the water quality varies from good to moderate with low potential for nuisance algal blooms. Lake Union typically has values within the moderate water quality range.

Lake Sammamish is the only one of the three lakes with a management plan and designated water quality goals. The plan calls for an annual volume weighted total phosphorus concentration (VWTP) of 22 µg/L or less. The south lake station has met this goal with a VWTP of 21 µg/L, while the north station had a VWTP of 22µg/L.

Influencing factors: In this region, phosphorus is most often the nutrient that promotes algal growth. The more phosphorus that can be stopped from entering lakes, the less chance that potentially toxic, algal bloom will grow. Phosphorus can be managed through well-designed drainage systems, maintenance of sewer infrastructure, changing homeowner and business behaviors using education and incentives and replacing watershed septic systems with sewers.

Existing DNRP response: King County will continue to monitor these lakes as part of its ongoing, Major Lakes Ambient Monitoring Program. This program is designed to track how lakes respond over time to various activities and inputs from the watersheds through influent streams, lake nutrient cycles, ecological interactions, and seasonal or year-to-year variability in weather. The goal of 100 percent of the three major lakes being within the range of moderate to low risk of potential algal blooms has been met. If the lakes begin to show serious deterioration in terms of their beneficial uses, actions will be taken to further investigate causes and plans will be made.

Priority new actions: Continual changes to data analysis and Web site reporting will provide current and accessible information for the management of these resources.

Back to top