The research was carried out on a small (10.5 ha) and shallow (2.5 m) Lake Gągławeckie (Gągławki). The drainage basin of Lake Gągławeckie is 348.3 ha. Forests land comprises the largest portion of this area, i.e. 66.7%, arable land 18.9%, grass land 7.5% and build area 2.9%. The waters were characteristic of a high content of phosphorus, up to 0.285 mg dm^–3, nitrogen up to 4.39 mg ∙ dm^–3 and calcium – 97.1 mg ∙ dm^–3. The reason for the lake’s high trophic level was no doubt the excessive loading from the drainage basin. The actual nutrient runoff from the drainage basin to the lake exceeded the critical loads, as defined by Vollenweider. Low quality of the lake’s waters and the parallel high external loading indicate that preventive measures should be taken, aimed at reducing the external loading.

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