CoFish: co-designing citizen science between fishers and scientists to monitor the phosphorus distribution across two Lake Geneva basins

Background Eutrophication, followed by re-oligotrophication during lake restoration, in many peri-alpine lakes has caused important changes to the functioning and biodiversity of freshwater ecosystems. In Lake Geneva, total phosphorus (TP) concentration has been reduced since the eutrophic years, and is now close to the upper value of the target range of 10-15 µg/L. For over 60 years the lake has been monitored at SHL2, the central and deepest point in the Eastern basin, complemented by data from GE3 in the Western basin. Selection of these reference points was based on a lake-wide analysis of TP in the 1950s. Fishers have for some time expressed concerns that further reductions in TP could damage the sustainability of their livelihoods. They have called for a re-evaluation of the historical sampling points to determine whether SHL2 and GE3 can still be considered representative in terms of nutrient concentration of the lake. Results Here, we present the scientific and societal impacts of CoFish, a co-designed research project between scientists and fishers of Lake Geneva. To reassess the spatial variability of TP we applied a low-cost method to collect integrated water samples across the lake, using stoppered hosepipes as a collection instrument. In this article, we present four key messages: i) There is spatial variation in phosphorous levels, and in most cases the two points fall withinan acceptable range of variability; ii) The concentrations of phosphorus are generally low across the lake in ranges that could have an impact for plankton development. iii) Citizen science can complement long-term monitoring, allowing for instance for better spatial coverage of environmental data; iv) The co-design process resulted in community empowerment, a willingness to further collaborate. Conclusions The management implications of this work are that using a single reference station as being representative for the lake as a whole is not straightforward. In the discussion we advocate for a re-evaluation of the TP targets, given radical changes in the lake`s physical structure and food web. We further highlight the important role of engaging fishers in citizen science, which resulted in bridging existing gaps between lake management, science and fisheries, providing a broader basis for lake conservation.