# Lake retention time

Lake retention time (also called the residence time of lake water, or the water age or flushing time) is a calculated quantity expressing the mean time that water (or some dissolved substance) spends in a particular lake. At its simplest, this figure is the result of dividing the lake volume by the flow in or out of the lake. It roughly expresses the amount of time taken for a substance introduced into a lake to flow out of it again. The retention time is especially important where pollutants are concerned.

## Global retention time

The global retention time for a lake (the overall mean time that water spends in the lake) is calculated by dividing the lake volume by either the mean rate of inflow of all tributaries, or by the mean rate of outflow (ideally including evaporation and seepage). This metric assumes that water in the lake is well-mixed (rather than stratified), so that any portion of the lake water is much like any other. In reality, larger and deeper lakes are generally not well-mixed. Many large lakes can be divided into distinct portions with only limited flow between them. Deep lakes are generally stratified, with deeper water mixing infrequently with surface water. These are often better modeled as several distinct sub-volumes of water.[1]

## More specific residence times

It is possible to calculate more specific residence time figures for a particular lake, such as individual residence times for sub-volumes (e.g. particular arms), or a residence time distribution for the various layers of a stratified lake. These figures can often better express the hydrodynamics of the lake. However, any such approach remains a simplification and must be guided by an understanding of the processes operating in the lake.

Two approaches can be used (often in combination) to elucidate how a particular lake works: field measurements and mathematical modeling. One common technique for field measurement is to introduce a tracer into the lake and monitor its movement. This can be a solid tracer, such as a float constructed to be neutrally buoyant within a particular water layer, or sometimes a liquid. This approach is sometimes referred to as using a Lagrangian reference frame. Another field measurement approach, using an Eulerian reference frame, is to capture various properties of the lake water (including mass movement, water temperature, electrical conductivity and levels of dissolved substances, typically oxygen) at various fixed positions in the lake. From these can be constructed an understanding of the dominant processes operating in the various parts of the lake and their range and duration.[1]

Field measurements alone are usually not a reliable basis for generating residence times, mainly because they necessarily represent a small subset of locations and conditions. Therefore, the measurements are generally used as the input for numerical models. In theory it would be possible to integrate a system of hydrodynamic equations with variable boundary conditions over a very long period sufficient for inflowing water particles to exit the lake. One could then calculate the traveling times of the particles using a Lagrangian method. However, this approach exceeds the detail available in current hydrodynamic models and the capacity of current computer resources. Instead, residence time models developed for gas and fluid dynamics, chemical engineering, and bio-hydrodynamics can be adapted to generate residence times for sub-volumes of lakes.[1]

## Renewal time

One useful mathematical model the measurement of how quickly inflows are able to refill a lake. Renewal time is a specific measure of retention time, where the focus is on 'how long does it take to completely replace all water in a lake.' This is modeling can only be done with an accurate budget of all water gained and lost by the system. Renewal time simply becomes a question how quickly could the inflows of the lake fill the entire volume of the basin (this does still assume the outflows are unchanged). For example if Lake Michigan was emptied, it would take 99 years for its tributaries to completely refill the lake. [2]

## List of residence times of lake water

The residence time listed is taken from the infobox in the associated article unless otherwise specified.

Lake Location Basin countries Residence time
Stausee Ferden Ferden, Valais Switzerland 36 hours
Lake Wohlen / Wohlensee Canton of Berne Switzerland 2.1 days
Lake Hévíz Hévíz Hungary 3 days
Lake St. Clair Great Lakes Canada, United States 7 days (2-30 days)
Lake Arapuni North Island New Zealand 1 week
Milton Pond Strafford County, New Hampshire, York County, Maine United States 11.1 days
Gibson Lake Gibson Generating Station, Princeton, Indiana United States 2 weeks
Råcksta Träsk Sweden 2-3 weeks
Lake Sagami Kanagawa Japan 0.05 year
Lake Cristallina Ticino Switzerland 2-4 weeks
Northeast Pond Strafford County, New Hampshire; York County, Maine United States 23.7 days
Brandy Pond Naples, Maine United States 34 days
Champagne Pool Waiotapu, North Island New Zealand 34 days
Prospect reservoir Prospect, New South Wales Australia 30-40 days
Sicklasjön Sweden 0.1 year
Devils Lake Lincoln County, Oregon United States 0.15 years
Lough Derg Ireland 0.15 years
Derwent Water Cumbria United Kingdom 55 days
Lake Biel / Bielersee / Lac de Bienne Canton of Berne Switzerland 58 days
Veluwemeer Netherlands 2 months
Hacksjön Sweden 0.2 years
Kamloops Lake British Columbia Canada ca. 0.2 years (20-340 days)
Malham Tarn North Yorkshire, England United Kingdom 11 weeks
Lac d'Anterne Passy, Haute-Savoie France 90 days
Graham Lake Hancock County, Maine United States 3 months
Grand Lac de Clairvaux Jura department, Franche-Comté France 3 months
Laduviken Sweden 3 months
Esthwaite Water Lake District, Cumbria United Kingdom 0.26 years
Trehörningen Huddinge, Southern Stockholm County Sweden 0.27 years
Lac de Divonne Divonne-les-Bains, Ain France 100 days
Lake Lesina / Lago di Lesina Province of Foggia, Apulia Italy 100 days
Seeweidsee Canton of Zurich Switzerland 100 days
Hüttnersee Hütten, Canton of Zurich Switzerland 120 days
Lake Lauerz / Lauerzersee Canton of Schwyz Switzerland 0.3378 years
Morris Lake Halifax Regional Municipality, Nova Scotia Canada 4.1 months
Sobradinho Reservoir Brazil 0.35 years
Balch Pond Carroll County, New Hampshire; York County, Maine United States 136 days
Magelungen Sweden 4-5 months
Russell Lake Halifax Regional Municipality, Nova Scotia Canada 4.6 months
Loweswater Lake District, Cumbria United Kingdom 150 days
Lappkärret Sweden 5 months
Lough Feeagh County Mayo Ireland 0.47 year
Egelsee Bubikon, Canton of Zurich Switzerland 180 days
Lac de Vouglans France 180 days
Mettmenhaslisee Canton of Zurich Switzerland 180 days
Albysjön Sweden 0.5 year
Chesuncook Lake Piscataquis County, Maine United States 6 months
Clinton Lake DeWitt County, Illinois United States 6 months
Flagstaff Lake Somerset County and Franklin County, Maine United States 6 months
Lake Coeur d'Alene Northern Idaho United States 0.5 years
Lac de Saint-Point Doubs department, Franche-Comté France 200 days
Kyrksjön Sweden 7 months
Newnan's Lake Gainesville, Florida United States 0.6 years
Staples Pond Temple, Maine United States 8.2 months
Lac Cornu Chamonix-Mont-Blanc, Haute-Savoie France 250 days
Lac du Brévent Chamonix, Haute-Savoie France 250 days
Lake Silvaplana / Silvaplanersee / Lej da Silvaplauna Engadin, Grisons Switzerland 250 days
Loch Awe Argyll and Bute, Scotland United Kingdom 0.7 year
Långsjön Sweden 9-10 months
Lake Sarnen / Sarnersee Obwalden Switzerland 0.8 years
Lake Lovozero Kola Peninsula, Murmansk Oblast Russia 10 months
Drevviken Sweden 10-11 months
Mörtsjön Sweden < 1 year
Judarn Bromma, Stockholm Sweden 11 months
Coniston Water Lake District, Cumbria United Kingdom 340 days
Ullswater Lake District, Cumbria United Kingdom 350 days
Khanka Lake Heilongjiang Province, China and Primorsky Krai, Russia China, Russia 1 year
Lake Monona Dane County, Wisconsin United States 1.1 years
Long Lake Maine United States 1.1 years
Mooselookmeguntic Lake Franklin County, Maine United States 1.1 years
Greifensee Canton of Zurich Switzerland 408 days
Nainital Lake Uttarakhand India 1.16 years
Manasbal Lake Kashmir Valley India 1.2 years
Lake Zurich / Zürichsee Switzerland 440 days
Tegernsee Bavaria Germany 1.28 years
Deer Creek Reservoir Utah United States 1.3 year
Orlången Huddinge Sweden 1.33 years
Haweswater Reservoir Lake District, Cumbria United Kingdom 500 days
Loch Shiel Lochaber, Highland, Scotland United Kingdom 1.37 year
Lake Walen /Walensee / Lake Walenstadt St. Gallen, Glarus Switzerland 1.4258 years
Keoka Lake Maine United States 1.5 years
Kootenay Lake British Columbia Canada 1.5 years
Lake Murten /Lac de Morat /Murtensee Canton of Fribourg, Vaud Switzerland 1.6 years
Oeschinen Lake Bernese Oberland Switzerland 1.61 years
Lac de Lessy Haute-Savoie France 600 days
East Grand Lake Maine / New Brunswick Canada, United States 1.7 years
Lake Ikeda Kyūshū island Japan 1.7 years
Lake Poyang China 0.173 years[3]
Faaker See Carinthia Austria 1.8 years
Ossiacher See / Lake Ossiach Carinthia Austria 1.8 years
Varese Lake/Lago di Varese Province of Varese, Lombardy Italy 1.8 years
Long Lost Lake Clearwater County, Minnesota United States 1.8 years
Ältasjön Älta Sweden 1.8 years
Lake Thun / Thunersee Canton of Berne Switzerland 684 days
Green Lake Maine United States 1.9 years
Gömmaren Sweden 1.9 yrs
Loch Lomond Dunbartonshire, Central Scotland Scotland, United Kingdom 1.9 years
Lake Balaton Hungary Hungary 2 years
Lake Rotoroa Hamilton, Waikato, North Island New Zealand approx. 2 years
Lake Tūtira Hawke's Bay, North Island New Zealand 2 years
Türlersee Canton of Zurich Switzerland 730 days
Pfäffikersee Canton of Zurich Switzerland 2.085 years
Caniapiscau Reservoir Quebec Canada 2.2 years
Lake Sils / Silsersee /Lej da Segl Engadin, Grisons Switzerland 2.2 years
Wilersee Canton of Zug Switzerland 2.2 years
Great Pond Maine United States 2.3 years
Moberly Lake British Columbia Canada 2.4 years
Päijänne Finland 2.5 years
Lake Erie North America Canada, United States 2.6 years
Rangeley Lake Franklin County, Maine United States 2.6 years
Lake Brienz / Brienzersee Canton of Berne Switzerland 2.69 years
Ammersee / Lake Ammer Upper Bavaria Germany 2.7 years
Großer Plöner See Schleswig-Holstein Germany 3 years
Paudash Lake Haliburton County, Ontario Canada 3 years
Moosehead Lake Maine United States 3.1 years
Trekanten Sweden 3.1 years
Great East Lake Carroll County, New Hampshire; York County, Maine United States 3.3 years
Lake Champlain North America Canada, United States 3.3 years
Flathead Lake Montana United States 3.4 years
Lake Lucerne /Vierwaldstättersee Central Switzerland Switzerland 3.4 years
Lake Winnipeg Manitoba, Canada Canada 3.5 years
Lac de Paladru Isère France 3.6 years
Lake Hallwil / Hallwilersee Aargau Switzerland 3.9 years
Flaten southern Stockholm Sweden 4 years
Lake Annecy / Lac d'Annecy Haute-Savoie France 4 years
Lake Maggiore / Verbano / Lago Maggiore Lombardy and Piedmont, Italy; Canton Ticino, Switzerland Italy, Switzerland 4 years
Todos los Santos Lake Chile 4 years
Lake Baldegg / Baldeggersee Canton of Lucerne Switzerland 4.2 years
Lake Iseo / Lago d'Iseo Lombardy Italy 4.2 years
Lake Constance / Bodensee Germany, Switzerland, Austria Germany, Switzerland, Austria 4.3 years
Corey Lake Michigan United States 4.4 years
Elk and Beaver Lakes Saanich, British Columbia Canada 4.4 years (Elk Lake),
Lake Como Lombardy Italy 4.5 years
Lake Mendota Wisconsin United States 4.5 years
Sea of Galilee Israel 5 years
Walden Pond Massachusetts United States 5 years [4]
Bannwaldsee Allgäu, Bavaria Germany 5.2 years
Sebago Lake Cumberland County, Maine United States 5.1 to 5.4 yrs
Kennisis Lake Haliburton Highlands, Ontario Canada 5.26 years
Bay Lake Crow Wing County, Minnesota United States 4-7 years
Lake Biwa / 琵琶湖 Japan 5.5 years
Jordan Pond Hancock County, Maine United States 6 years
Lago di Mergozzo Piedmont Italy 6 years
Lake Ontario North America Canada, United States 6 years
Lac la Nonne Alberta Canada 6.5 years
Lago di Candia Province of Turin Italy 6 or 7 years
Ägerisee Canton of Zug Switzerland 6.8 years
Loch Morar Morar, Lochaber, Highland, Scotland United Kingdom 6.87 years
Lake Powell Utah/Arizona United States 7.2 years
Millstätter See / Lake Millstatt Carinthia Austria 7.5 years
Moose Lake Alberta Canada 7.5 years
Schaalsee Schleswig-Holstein Germany 5 to 10 years
Iliamna Lake Lake and Peninsula Borough, Alaska United States 7.8 years
Lac du Bourget Savoie, France France 8 years
Odell Lake Klamath County, Oregon United States 8 years
Lake Lugano /Lago di Lugano Ticino, Lombardy Switzerland, Italy 8.2 years
Lake Neuchâtel / Lac de Neuchâtel / Neuenburgersee Switzerland 8.2 years
Lake Orta /Lago d’Orta /Cusio Piedmont Italy 8.9 years
Weissensee Carinthia Austria 9.2 years
Quesnel Lake British Columbia Canada 10.1 years
Schweriner See Mecklenburg-Vorpommern Germany 10.1 years
Lake Taupo Taupo District, Waikato region, North Island New Zealand 10.5 years
Wörthersee / Lake Wörth west of Klagenfurt Austria 10.5 years
Lake Chelan Washington United States 10.6 years
Lake Geneva Switzerland, France Switzerland, France 11.4 years
Lake Wakatipu Queenstown-Lakes District, Otago Region, South Island New Zealand c. 12 years
Higgins Lake Michigan United States 12.5 years
Crescent Lake Klamath County, Oregon United States 13 years
Lake Zug / Zugersee Switzerland 14.7 years
Müritz Mecklenburg-Vorpommern Germany 15 years (?)
Western Brook Pond Gros Morne National Park, Newfoundland, Newfoundland and Labrador Canada 15.4 years
Lake Sempach / Sempachersee Canton of Lucerne Switzerland 16.9 years
Skaneateles Lake New York United States 18 years
Cayuga Lake New York United States 18.2 years
Bear Lake Idaho, Utah United States 19.6 years
Green Lake Green Lake County, Wisconsin United States 21 years
Lake Starnberg /Starnberger See Bavaria Germany 21 years
Lake Huron North America Canada, United States 22 years
Lake Garda / Lago di Garda Northern Italy Italy 26.8 years
Waldo Lake Cascade Mountains United States 32 years
Crystal Lake Benzie County, Michigan United States 30 to 60 years
Lake Columbia Jackson County, Michigan United States 47 years
Okanagan Lake British Columbia Canada 52.8 years
Lake Ohrid Republic of Macedonia 70 years
Lake Michigan United States United States 99 years
Arendsee Saxony-Anhalt Germany 100 years
Gull Lake Alberta Canada >100 years
Lake Yosemite California United States 121 years
Great Bear Lake Northwest Territories Canada 124 years
Crater Lake Oregon United States 157 years
Lake Superior North America Canada, United States 191 years
Caspian Sea Azerbaijan, Iran, Kazakhstan, Russia, Turkmenistan 250 years
Lake Baikal Russia 330 years
Lake Tahoe California, Nevada United States 650 years
Lake Titicaca Peru, Bolivia 1343 years
Lake Eucumbene Snowy Mountains, New South Wales Australia 1953 years
Lakes Qaban Russia 2000 years
Lake Tanganyika Burundi, DR Congo, Tanzania, Zambia 5500 years
Lake Vostok Antarctica 13300 years