Simulators / APES Unit 8 / Topic 8.5
Lake Eutrophication Simulator
Lake Marrow turns green every summer and last August the fish died. You have eight years and two coins a year. Pay to cut the nutrient sources, or pay to hide the symptoms, and see what the lake does. Free, with no login.
Where the phosphorus comes from
P units per year entering the lake. The forest is natural background; the other four sources come from people. Illustrative data: values are hypothetical.
Phosphorus in the lake, L
Bottom dissolved oxygen (mg/L)
How eutrophication works (the chain behind the model)
The model, in one minute. Each year the lake keeps half of last year's phosphorus and receives a new load: L = half of last L (rounded down) + total load. Algae A = L divided by 2 (rounded down). Bottom oxygen DO = 9 minus (A divided by 2, rounded down), never below 0. Hypoxic means DO below 2 mg/L. A fish species survives only if DO meets its need: trout 7, smallmouth bass 5, yellow perch 3, carp 1.
What the model leaves out. Phosphorus usually limits algae in fresh water, while nitrogen often limits coastal waters. Real lakes also release phosphorus stored in the sediment, which is one reason recovery lags, and some blooms make toxins. The "keep half" rule stands in for the slow recovery. Lake Marrow is fictional and every number is hypothetical, so use the model to see the cause-and-effect pattern, not to predict a real lake.
Take it to class
Free teacher guide and student sheet
Use this simulator as a 30 to 40 minute lesson on Topic 8.5. The free guide has a pacing plan, a student recording sheet, discussion questions, and a claim, evidence, and reasoning prompt, and it ships with an offline copy of the simulator.
Ready to run
Students open this page on any laptop or phone. No login, no download, and nothing to install.
Cause versus symptom
The budget forces the trade-off from the CED: cutting a nutrient source is not the same as treating low oxygen.
Full activity in Unit 8
The Lake Commission print and digital activity, with the case file, watershed map, and answer key, is part of the Unit 8 bundle.
About the model: one nutrient, five sources, and four fish species. It is built to show the pattern of eutrophication and the lag in recovery, not to predict a real lake. For an AP course, pair it with real data such as dissolved oxygen profiles, algae counts, and nutrient loads from a lake your students know.