A diatom transfer function based on data from 152 lakes in northwest Europe is derived using the technique of weighted-averaging partial least squares (WAPLS) and applied to Lake Søbygård, a shallow, hypertrophic Danish lake, to infer past changes in epilimnetic total phosphorus (TP) concentrations since the 1930s. The results show that the two-component WAPLS model has low prediction errors (RMSEP) 0.21 log 10 TP units) and is applicable to lakes distributed throughout northwest Europe, covering a TP range 10-1000 µg TP L -1 . The example shows how the method can provide an estimate of baseline conditions and rates of enrichment, allowing manag-ers to set realistic targets for lake restoration.