Tool · free
Carlson TSI calculator - lake trophic status
The Carlson TSI index turns a lake’s productivity into a single number (0-100). You can calculate it from any of three indicators - transparency (Secchi disk), chlorophyll-a or total phosphorus - or from the full set.
Enter at least one indicator.
Formulas
The relationships are logarithmic (SD in metres, Chl and TP in µg/l):
TSI(SD) = 60 − 14.41 · ln(SD)TSI(Chl) = 30.6 + 9.81 · ln(Chl)TSI(TP) = 4.15 + 14.42 · ln(TP)
Ideally all three give a similar result. A large discrepancy signals that something other than algae affects transparency (e.g. mineral suspension) - then trust the TSI from chlorophyll and phosphorus more.
Frequently asked questions
Which indicator should I enter if I only have one?
One is enough - you can calculate TSI from transparency alone (Secchi disk), from chlorophyll-a or from total phosphorus. The fullest picture comes from all three: the divergence between them is itself information about what limits algal production.
How do I read the TSI result?
Scale 0-100: below 40 - oligotrophic lake (poor, clear); 40-50 - mesotrophic; 50-70 - eutrophic (fertile, blooms); above 70 - hypertrophic. The higher the value, the greater the productivity.
Is one measurement enough?
TSI is best calculated from growing-season data and as a time series - a single reading can be misleading (e.g. after rainfall transparency drops due to mineral suspension, not algae).
You calculated once - now track it over time
A single result says little; the value shows in a series of measurements. In LimnoLog you record readings in the field (also offline), and they instantly turn into charts, exports and a public link.
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