Aim of the study:
The Gala Lake, which has a status of National Park and is an under-protection area, is the one of the most important natural stagnant water bodies in the Marmara Region of Türkiye. However, it is under effect of a significant agricultural stress sourced by mainly paddy cultivation. In this research, the epiphytic diatoms of Gala Lake were investigated, and the trophic status of the lake was assessed by applying the Biological Diatom Index (BDI).

Material and methods:
Epiphytic diatom samples were collected from the submerged macrophytes from 5 selected locations on the lake (G1–G5) with different ecological characters observed to be exposed to different pollution pressures.

Results and conclusions:
As a result of taxonomic data, 37 diatom species were recorded by identifying a total of 2095 valves, and Cyclotella meneghiniana, Bacillaria paxillifera, and Navicula recens were found as the most dominant species for the Gala Lake. According to the results of bioindication data, Gala Lake was found to be in a "eutrophic state"—"having poor water quality" in terms of applied BDI.