The dataset includes Chlorophyll-a concentration in μg/L. Measurements of Chl a were made on discrete water samples collected monthly in the upper 20 meters layer at sampling station Ghiffa (45°58’30’’N; 8°39’09’’E), corresponding to the lake deepest point, from January 1984 to December 2018. Chl-a measurements derived by spectrophotometric technique in the period from January 1984 to December 2009, while from January 2010 to December 2018 measurements derived from vertical profiling instrument (FluoroProbe).

Chl-a concentrations were measured by spectrophotometry following the APAT IRSA 9020 method. A measured volume of water from each treatment was filtered on a GF/C glass fibre filter and frozen until the analysis. The filters were extracted with 5 ml of a mixture of acetone and MilliQ water (90:10), centrifuged and then absorbance spectra performed with a spectrophotometer. The Chl-a concentration was then obtained with the application of the trichromatic equation proposed by Ritchie (2008). From 2010 the Chlorophyll a concentration was simultaneously measured also with bbe-Fluoroprobe. The FluoroProbe III measures the chlorophyll-a of suspended phytoplankton in vivo. The FluoroProbe was deployed vertically till 20 meters depth. The calculation of the distribution of the amount of Chlorophyll-a is performed by using previously stored fluorescence profiles of the known algal classes from the algae library of Lake Maggiore.

Ritchie R.J. (2008). Universal chlorophyll equations for estimating chlorophylls a, b, c, and d and total chlorophylls in natural assemblages of photosynthetic organisms using acetone, methanol, or ethanol solvents. Photosynthetica 46: 115–126.

These data were collected within the limnological campaigns on Lake Maggiore funded by the International Commission for the Protection of Italian-Swiss Waters (CIPAIS)