Tool · free
Carlson TSI calculator - lake trophic status
The Carlson TSI index converts a lake’s productivity to a common 0-100 scale. One of three indicators is enough: transparency (Secchi disk), chlorophyll-a or total phosphorus. Each gives its own result - you can enter all three and compare them.
Enter at least one indicator.
No data yet?
Load it in the app under "New project" → "From backup".
These calculations are stored in this browser only and disappear when you clear the site data. Download them or move them into a project - there they stay for good.
How to move this into a project of your own
- Download the table - the CSV file lands in your Downloads.
- Create a free account: an e-mail address and a password is all it takes.
- In the app choose "New project" → "From your sheet" and point it at the downloaded file. The station and the parameters are created for you, and LimnoLog computes the calculated ones itself.
| Date | Time | Secchi [m] | Chl-a [µg/l] | TP [µg/l] | Mean (aux.) |
|---|
The current reading is only a preview - it joins the list and the file only once you add it with the button.
Kept in this browser only. Nothing is sent to a server - clearing the site data removes this table.
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)
Three results are three separate measures of the same phenomenon, not three attempts at one number. When they are close, the assessment is more reliable. When they diverge, do not average them - the divergence is information: usually something other than algae limits transparency (mineral suspension, water colour), or the algae are not using the phosphorus (nitrogen shortage, grazing by zooplankton, light). For classification, Carlson and NALMS recommend the chlorophyll-a TSI, because chlorophyll measures algal biomass directly. That is why the class is shown for each component separately, and a divergence note appears when the components differ by at least 10 points (that is what doubling phosphorus or halving Secchi depth gives; an indicative threshold, NALMS gives no number). The mean of the three is shown for reference only and gets no class - it would mix a good measure with two weaker ones.
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. The class is given for each component separately - when they differ, that is information about the lake, not a calculation error.
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.
Open the app Explore LimnoLog featuresRead more