## 1 Introduction  
Phosphorus (P) is one of the nutrients necessary for aquatic organisms to develop and grow. However, its excess in the aquatic environment causes eutrophication with a number of negative effects on ecosystems, such as oxygen depletion, alkaline pH, and massive blooms of phytoplankton, including toxic cyanobacteria [1]. The results are changes in biodiversity, water quality deterioration, and limitations in the use of water bodies [1; 2; 3]. Therefore, external solutions to combat P transport to water bodies are employed and developed [4], such as inflow treatment [5], buffer zones [6], and permeable reactive barriers [7]. In lakes, however, a large pool of phosphorus is usually stored in the sediment, part of which being released to the water column, leading to an internal phosphorus loading [8; 9]. Thus, strategies to in situ manage P excess in water bodies are applied [4], frequently aiming at immobilizing the dissolved P (orthophosphates, OP) by the addition of P binding agents into the water column (or sediments) and reducing the P flux from the sediment [10]. Substances used for this purpose are usually aluminum (or iron) salts or lanthanum-enriched clay [11; 12; 13; 14]. The application of P binding agents may lead to some non-target effects on the lake ecosystem. Although they are typically dosed and distributed evenly to the lake water column, the accumulation of binding agents in specific lake areas has been reported, e.g., due to wind effects [15; 16; 17]. Increased concentrations of ammonia [18] and metals [17; 19] have also been observed. What is more, the stability of the P fixation on the binding materials can be reduced under variations of physio-chemical conditions [20; 21; 22] and/or under the effect of physical and biological processes, especially in shallow lakes, where wind resuspension strongly affects the agent interactions with sediments [23; 24; 25]. Aging processes can further lead to reduced P sorption on the materials applied [26; 27]. Adverse effects on the aquatic organisms caused by the reactive agents have also been reported [28; 29; 30]. At the same time, the need for P recovery and closing the P cycle has been increasingly noticed [31; 32; 33] also in the area of lake restoration [34; 35]. P management strategies enabling P removal from the aquatic ecosystem and its recovery for further reuse are regarded to have priority among lake restoration options [36]. Technologies for not only inactivating but permanently removing P from the catchment have been suggested and developed for flowing waters, e.g., small streams [37; 38]. Taking this into consideration, we developed a novel approach for P removal from water bodies enabling the application of a binding agent into the water column for a given time, using packaging or a carrier, to allow P sorption and the subsequent removal of the carrier together with the P-loaded binding agent (Figure 1). Such a measure ensures P inactivation and P removal from the ecosystem and eliminates risks related to the disposal of the binding agent in the aquatic environment. We thus called this approach a non-invasive phosphorus removal [39]. The P binding agent can be applied to a water body in a given site at target depth and, for a given period, without the risk of being allocated. At the same time, the removal of the agent together with the inactivated orthophosphate (OP) opens the chances for P recovery and reuse. Our first attempts to develop solutions for non-invasive P removal were based on a simple technical concept of placing the P binding material in packaging made of a porous elastic fabric [40] (similar to the idea developed shortly afterwards by [PERSON]  
Figure 1: Principle of the non-invasive phosphorus removal approach. called \"tea-bags\").