Aquatic ecosystems are attractive sites for recreation. However, human presence at or on aquatic ecosystems can have a range of ecological impacts, creating trade-offs between recreation as ecosystem service and biodiversity conservation. There is currently no synthesis of evidence regarding the ecological impacts associated with various forms of aquatic recreation, to compare the magnitude of effects between types of recreation. Therefore, conservation conflicts surrounding water-based recreation are difficult to manage. We conducted a global meta-analysis, differentiating various recreational impacts and the type of recreational uses in four categories: shore use, shoreline angling, swimming and boating; and studied ecological impacts directed at three levels of biological organization: individuals, populations, and communities. We screened over 13,000 articles and identified 94 suitable studies providing 701 effect sizes for inclusion in the meta-analysis. Aggregated across all animal and plant taxa, impacts of boating and shore use resulted in highly significant effects on almost all levels of biological organization. Regarding taxonomic groups, the most negative effects of water-based recreation were observed in invertebrates, whereas effects on birds were most pronounced at individual levels and not significant at community levels. From a conservation perspective, fostering water-based recreation and the ecological services they provide must be balanced with ecological impacts associated with the activities. Although generalizations are challenging, local scale effects of activity-specific constraints seem unlikely to be effective if other forms of water-based recreation continue.

Systematic literature research using multiple data bases

We conducted a systematic literature search from November 2018 until February 2019 following the guidelines for systematic research by Siddaway, Wood [47]. We searched both peer-reviewed and gray literature in different languages to compile the best available evidence base. We constructed a search term containing synonyms for recreation AND aquatic AND impacts AND environment. The following search term was used for the literature research in the Web of Science Core collection:

((recreation* leisure (*shore NEAR/1 development) pleasure sport* tourist (human near/1 wildlife) (outdoNEAR/0 activity) (UV NEAR/1 (filter* protection screen)))

AND

(aquatic water* lake* river* stream* freshwater* marine riparian littoral coast* beach* reed* shore*)

AND

(impact* disturb* effect* affect* consequence* comparison* change* modification* alter* influence* behavio*r reaction* avoid* survival abundance fitness FID (flight NEAR/0 (initiation NEAR/0 distance)) population biodiversity conservation stress pressure trampl* litter* community assemblages introduction toxic pollution eutrophication (nutrient NEAR/1 input) endocrine reproducti*)

AND

(biodiversity (species NEAR/1 richness) sediment* (water NEAR/0 (quality chemistry)) ecolog* animal* vegetation plant* macrophyte* wildlife *bird* *fowl mammal* fish* crayfish amphibia* reptile* insect* *invertebrat* habitat* biotop* ecosystem* invasive (food NEAR/0 web)))

NOT medic* NOT antibiotic* NOT cattle NOT coli

Literature regarding archaea (e.g. E.coli) was excluded because these focused on human health issues and were in addition often associated with wastewater treatment plants as additional or only source besides recreation as source.

We adapted the search terms for seven different literature databases (see supplement for search term variations) and yielded 13.115 articles: Web of Science Core Collection n = 6.937, Scopus n = 4.206, BioOne n = 1.056, Conservation Evidence n = 39, BASE n = 596, and ASFA n = 45. List of all search terms for each data base is given in the in the Supplemental protocol S1

#Coding procedure with all coded variables (metadata) are avainlable in the supplemental material (S1 protocol) via https://doi.org/10.5281/zenodo.5110023

#R code for statistical analysis of the mata-analysis of the manuscript RSPB-2020-3155 entitled "Ecological impacts of water-based recreational activities on freshwater ecosystems: a global meta-analysis" in Proceedings B by Schafft et al. is also provided via https://doi.org/10.5281/zenodo.5110021