## 1 Introduction  
The inflow of various chemical compounds from a catchment determines the eutrophication status of lakes, which is a natural and long-lasting phenomenon leading to their degradation [1, 2]. The rate of this process and the concentrations of the main elements responsible for the increase in water trophic state can be influenced by many factors, such as water dynamics, hydrology, morphometry, and basin usage [3, 4]. Human activities, such as urbanization, industrialization, or agricultural use of areas adjacent to water bodies, accelerate eutrophication and can cause the degradation of water quality [5, 6]. Lakes situated in urban and agricultural areas are particularly endangered, as they hold the role of receiving water from municipal, industrial and precipitation wastes and nutrients from leaky septic tanks and agricultural fields (such as mineral fertilizers, plant protection products, pesticides). The load of nutrients introduced by sewage can be high that it disturbs the biological balance and disrupts the biogeochemical processes of an ecosystem [7, 8, 9]. Nutrients flowing into the aquatic ecosystems participate in various processes, collectively referred to as the circulation of matter. One of the main processes is the uptake of the dissolved mineral forms of nitrogen and phosphorus by primary producers for photosynthesis and their subsequent processing and release in the food web [10]. Moreover, biogenic elements in the form of organic compounds, suspensions and complexes with iron, aluminum and calcium are subject to sedimentation and accumulation in bottom sediments. The withdrawal of nutrients to bottom sediment is temporary [11, 12]. A significant portion of the substancesaccumulated in the sediment are processed by living organisms and returned to circulation. This process is called \"internal loading\" and is common in degraded lakes. In most aquatic ecosystems, the \"internal loading\" in the long term has a negative value, and in degraded water bodies, as a result of the significant accumulation of nutrients in sediment and exceeding the limits of the permissible external load for a reservoir, it becomes positive. This is the stage where the transport of elements from bottom sediment exceeds their precipitation. This phase is known as saprotrophy, i.e., the moribund state of the lake whereby it is unable to transform the excess organic matter and minerals within its structure and the organisms functioning in it. Disruption of the normal functions of a lake ecosystem is manifested primarily by massive algae and cyanobacterial blooms as well as oxygen deficits in the deeper parts of the reservoir [1]. The effect of an excessive increase in the fertilization levels of a lake is also elimination of the water body as an object utilized for communal and recreational purposes. The issue of accelerated eutrophication has generated a need for new remedy measures consisting of the protection of endangered reservoirs or restoration of those that have already been degraded [13]. [PERSON] et al. [14], [PERSON] [15], and [PERSON] et al. [16] provided many solutions that allow for the elimination or reduction of external sources of nutrients (protection of lakes) through technical (artificial aeration, removal of bottom sediments, selective removal of hypolimnon waters), chemical (phosphorus inactivation, sediment treatment) and biological (biomanipulation) methods carried out within a lake basin (lake restoration). Experiments conducted worldwide have proven that protective methods implemented within a catchment play the most important and essential role in improving the condition of the aquatic environment [17; 18]. The research of many authors [19; 20; 21] has shown that in the case of lakes where the internal fertilization of nitrogen (N) and phosphorus (P) water from bottom sediments has started, limiting the external load does not improve the water quality.