LAKE WASHINGTON

A iew of the lake with Mr. Rainiew in the background

Photo.
Photo: Y. Kurata  
 

A. LOCATION

Washington, USA. 47:0 -47:5 N, 122:0 -122:6 W; ca. 0 m above sea level.

B. DESCRIPTION

Lake Washington is a long, narrow lake located in an urbanized area close to Seattle. It covers an area of 88 km2 and is crossed by two floating bridges. The lake shore affords a good view of the snow-covered cone of Mt. Rainier. The climate around the lake is mild throughout the year with only sporadic snowfall in winter.
In 1916, a canal with locks and a fish ladder was made connecting the lake with the open sea to the west for navigation. The lake had been still oligotrophic in the late 1930's, but an increasing influx of urban sewage from the surrounding area caused rapid progress of eutrophication, as indicated by the frequent bloom of blue-green algae in summer since 1955. However, the construction of sewage treatment plants and the diversion of treated water through a 180 km-long pipeline, carried out in the five years from 1963 to 1968, have improved the quality of the lake water until it recovered almost completely in 1975. The chemical parameters of the lake water have remained quite stable for the past ten years, and the citizens of Seattle and neighboring cities enjoy swimming, fishing and sailing in the lake again.

C. PHYSICAL DIMENSIONS

     
    Surface area [km2] 88
    Volume [km3] 2.89
    Maximum depth [m] 65.2
    Mean depth [m] 32.9
    Water level Regulated
    Residence time [yr] 3.1-1.7
    Catchment area [km2] 1,274
     
 

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL Bathymetric map: Fig. NAM-09-01. Names of main islands: Mercer. Number of outflowing rivers and channels (name) 1 (Lake Washington Ship Canal).
D2 CLIMATIC Climatic data at Seattle, 1931-1960 (1) Mean temp. [deg C]
     
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    5.1 6.4 8.0 11.0 14.1 16.3 18.7 18.3 16.2 12.4 8.3 6.6 11.8
     
Precipitation [mm]
     
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    132 99 84 50 40 36 16 19 42 83 127 138 865
     
Number of hours of bright sunshine: 2,019 hr yr-1. Solar radiation: 11.77 MJ m-2 day-1. Snowfall: Intermittent (Q).

    Fig. NAM-09-01
    Bathymetric map (Q).
 

Water temperature [deg C](Q) Madison Park Station, 1982

     
    Depth[m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* 7.7 7.4 7.6 9.4 13.8 19.9 20.0 20.2 18.7 15.1 11.0 9.1
    * Surface.

    Fig. NAM-09-02
    Seasonal and vertical distribution of water temperature (Madison Park Station), 1982 (Q).
 

Freezing period: None. Mixing type: Monomictic. Notes on water mixing and thermocline formation Thermocline exists usually from late April or early May until early December.

E. LAKE WATER QUALITY (Q)

E1 TRANSPARENCY [m] Madison Park Station, 1982
     
    Depth[m]  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    7.2 7.0 5.7 4.4 2.6 6.4 6.4 5.9 5.6 5.4 6.6 6.9
     
E2 pH Madison Park Station, 1982
     
    Depth[m]  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* 7.20 7.26 6.25 8.19 9.02 8.75 8.38 8.22 8.18 7.71  7.42 7.27
    * Surface water.
E3 SS [mg l-1] Madison Park Station, 1982
     
    Depth[m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 1.19 1.35 1.52 3.99 5.52 - 1.27 1.92 2.98 1.81 1.64 1.86
    5 - - - 4.32 5.50 - 1.30 - 2.03 2.16 1.69 -
    10 1.47 1.51 1.58 3.61 2.79 - 1.38 2.01 1.99 2.03 1.54 1.50
    15 - - - 2.72 1.28 - 1.39 0.81 0.80 1.69 - -
    20 - - - - 0.86 - 0.69 0.71 0.78 0.65 1.56 -
    30 - - - - - - 0.58 0.59 0.87 0.58 0.90 1.58
    40 - - - - - - 0.30 0.56 0.62 0.76 0.90 1.40
    50 - - - - - - 0.40 0.56 0.64 0.93 1.52 1.47
    60 1.23 1.79 1.95 3.15 1.84 - 1.38 1.90 0.96 1.92 1.62 1.91
     
E4 DO [mg l-1] Madison Park Station, 1982
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 10.17 11.14 11.52  12.96 12.76  10.14  9.51 9.78 9.42  9.66 9.55 9.51
    5 - - - 12.84  12.72  10.99  9.51 9.88 9.38  9.64 9.55 -
    10 10.12 11.10  11.58  12.06  11.53 10.19 9.24 9.31 9.12 9.54 9.49 9.51
    15 - - - 11.44  11.09 9.79  8.56 7.51 9.06  6.77 - -
    20 - - - 10.97 9.93 8.84 8.17 7.45 6.83  9.45 - -
    30 - - - - 10.42 9.72 9.11 8.48 7.67 6.70 9.55 -
    40 - - - - - - 9.86 9.05 8.37  7.87 6.42 9.55
    50 - - - - - 9.84 9.61 8.57 8.19 6.99 5.99 9.35
    60 10.05  11.05 11.13  10.92 9.43 7.69  7.64 6.11 5.98 5.50 5.54 6.15
     
E6 CHLOROPHYLL CONCENTRATION [micro g l-1] Madison Park Station, 1982
     
    Depth[m]  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 0.40 0.61 3.08 11.61 19.96  2.40 3.22 2.53 3.03 5.64 4.00 3.18
    5 - - - 11.37  24.34 3.46 2.92 4.40 3.44 6.17 5.28 -
    10 0.57 0.61 3.52 8.61 11.47  3.44 2.79 3.87 2.61 7.32 4.18 3.32
    15 - - - 7.37 4.77 2.97 1.96 2.54 1.12 6.33 - -
    20 - - - - 2.38  1.34 1.48 1.52 0.90 0.83 4.66 -
    30 - - - - - 0.75 0.71 0.49 0.43 0.60 0.97 3.59
    40 - - - - - - 0.87 0.37 0.40 0.59 0.98 3.51
    50 - - - - - 0.61 0.70 0.31 0.28 0.74 1.09 3.30
    60 0.66 0.56 1.87 2.91 2.71  1.03 1.20 0.99 0.21 1.27 1.32 2.94
     
E7 NITROGEN CONCENTRATION Kjeldhal N [mg l-1] Madison Park Station, 1982
     
    Depth[m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 .24 .244 .203 .249 .322 .248 .213 .294 .268 .277 .299 .216
    5 - - - .289 .327 .317 .219 .256 .223 .254 .446 -
    10 .221 .266 .182 .249 .275 .311 .183 .256 .268 .277 .247 .171
    15 - - - .223 .236 .279 .195 .138 .189 .331 - -
    20 - - - - .178 .216 .207 .225 .242 .215 .247 -
    30 - - - - - .178 .178 .213 .175 .277 .194 .22
    40 - - - - - - .178 .294 .182 .231 .262 .156
    50 - - - - - .19 .225 .256 .189 .277 .232 .182
    60 .212 .216 .194 .151 .171 .197 .178 .313 .195 .277 .239 .192
     
E8 PHOSPHORUS CONCENTRATION Total-P [mg l-1] Madison Park Station, 1982
     
    Depth[m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 .027 .030 - .025 .029 .011 .009 .011 .012 .013 .012 .018
    5 - - - .026 .021 .015 .010 .012 .013 .010 .011 .015
    10 .028 .030 - .029 .013 .019 .009 .012 .012 .010 .011 -
    15 - - - .026 .010 .008 .009 .011 .007 .010 - -
    20 - - - - .016 .008 .009 .010 .006 .006 .012 -
    30 - - - - - .019 .017 .015 .014 .013 .023 .016
    40 - - - - - - .019 .025 .023 .022 .028 .017
    50 - - - - - .024 .022 .030 .030 .032 .030 .022
    60 .028 .032 - .043 .031 .026 .031 .045 .034 .041 .037 .026
     
E10 PAST TRENDS Secondarily treated sewage effluent had once been dumped into the lake from the city of Seattle and other small cities around the lake, until a diversion system was implemented in 1968. Certain chemical parameters were much different in the late 1950's and early to mid 1960's than they are today. Winter PO4 and total-P routinely reached a level of 50 micro g l-1. There has also been a temporal shift in peak chlorophyll concentration . In 1963, maximum values occurred in the summer with the bloom of the blue-green filament, Oscillatoria agardhii. Since sewage diversion, however, maximum phytoplankton biomass has occurred in spring when diatoms are in the greatest abundance, and so the maximum chlorophyll concentration tended to appear in late April through May. Oxygen depletion at the bottom during late summer continues to occur, but in a lesser degree since production has been reduced. When large summer blooms used to occur, surface pH became more alkaline than it does now, often reaching 9. The chemistry values for the lake have been fairly stable for the past ten years, and the year 1982 for which the data are given here is considered a typical year chemically.

F. BIOLOGICAL FEATURES

F1 FLORA Floating macrophytes: Nymphaea odorata. Submerged macrophytes Myriophyllum spicatum, Ceratophyllum demersum, Potamogeton spp., Elodea canadensis, Zanichellia palustris. Phytoplankton Spring Melosira italica, Fragilaria crotonensis, Stephanodiscus spp., Cyclotella pseudostelligera. Summer and autumn Aphanizomenon flos-aquae, Microcystis aeruginosa, Coelosphaerium haegilianum, Tabellaria flocculosum, Oociptis gigas.
F2 FAUNA Zooplankton Daphnia pulicaria, D. thorata, Diaptomus ashlandi, Epischura sp., Neomysis mercedis. Benthos: Various species of chironomids (not identified). Fish Oncorhynchus nerka, O. tshaorytscha, Salmo gairdneri, Micropterus salmoides, Perca flavescens, Lepomis gibbosus, Osmerus sp.
F5 FISHERY PRODUCTS Annual fish catch 1984: Not estimated*. * Sport-fishing only.
F7 NOTES ON THE REMARKABLE CHANGES OF BIOTA IN THE LAKE IN RECENT YEARS Change in phytoplankton from Oscillatoria dominance to diatom dominance since sewage diversion. Appearance and domination of Daphnia spp. since 1976. Appearance and spread of Myriophyllum in shallow water zones.

G. SOCIO-ECONOMIC CONDITIONS

G1 LAND USE IN THE CATCHMENT AREA 1984
     
    Area [km2] [%]
    Natural landscape
    Woody and 382 30
    herbaceous vegetation
    Agricultural land 127 10
    Residential area 765 60
    Total 1,274 100
     
Main types of woody vegetation Pseudotsuga menziesii forest; Alnus rubra forest. Main types of herbaceous vegetation: Pasture and grasslands. Main kinds of crops: Grasses for hay.
G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE 1982 Mainly residential and recreational use of the lake and shoreline. Boeing Company at the south end of the lake.
G3 POPULATION IN THE CATCHMENT AREA 1982
     
    Population Major cities
    Population density [km-2] (population)
    Total 1,500,000 1,180 Seattle (490,000), Bellevue
     
 

H. LAKE UTILIZATION

H1 LAKE UTILIZATION Navigation, tourism and recreation (swimming, yachting and sport-fishing).
H2 THE LAKE AS WATER RESOURCE 1984: Not used.

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS

I1 ENHANCED SILTATION Extent of damage: Not serious.
I3 EUTROPHICATION Nuisance caused by eutrophication Unusual bloom of Oscillatoria agardhii in the late 1950's to 1974; since gone from the lake. Nitrogen and phosphorus loadings to the lake Nitrogen mainly from agricultural and natural sources, and phosphorus mainly from domestic and agricultural sources.
I4 ACIDIFICATION
  • Extent of damage: Not serious.
 

J. WASTEWATER TREATMENTS

J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA
    c) Limited pollution with wastewater treatment.
J3 SANITARY FACILITIES AND SEWERAGE Municipal wastewater treatment systems Present (activated sludge; for domestic wastewater and rainwater).

K. IMPROVEMENT WORKS IN THE LAKE

K1 RESTORATION Diversion: All sewage effluent diverted from the lake in 1968 and disposed of elsewhere (Puget Sound).

M. LEGISLATIVE AND INSTITUTIONAL MEASURES FOR UPGRADING LAKE ENVIRONMENTS

M1 NATIONAL AND LOCAL LAWS CONCERNED Responsible authorities
  1. Municipality of metropolitan Seattle Main items of control
  2. Sewage treatment and disposal
 

N. SOURCES OF DATA

  1. Questionnaire filled by Dr. S. Abella by recommendation of Dr. W. T. Edmondson, Department of Zoology, University of Washington.
  2. Muller, M. J. (1982) Selected Climatic Data for a Global Set of Standard Stations for Vegetation Science. 306 pp. Dr. W. Junk Publishers, The Hague.