The effects of aquatic interventions on emotional and behavioral outcomes in children with autism spectrum disorder.

Children with autism spectrum disorder (ASD) commonly experience emotional and behavioral difficulties that may arise from atypical sensory processing, and the sensory properties of water closely correspond to these characteristics. We systematically evaluated the effects of aquatic interventions on four pre-specified outcome domains-emotion-related functioning, social-emotional functioning, behavioral outcomes, and quality of life-in children with ASD. Eight bibliographic databases and one trial registry were searched from inception to July 2026 using a two-concept strategy without language restriction, for studies involving children with ASD who received a structured aquatic intervention and reported a validated outcome. Methodological quality was assessed using RoB 2, ROBINS-I, and single-case design criteria, and the certainty of evidence was evaluated with GRADE. Owing to heterogeneous outcome instruments and the small number of controlled studies, a meta-analysis was not conducted; in accordance with the Synthesis Without Meta-analysis (SWiM) guideline, findings were synthesized narratively by domain, with the direction of effect and statistical significance tabulated and illustrated in an effect-direction (harvest) plot. Nineteen publications, describing up to 18 independent studies (approximately 320 participants in total from 10 countries, including non-ASD comparison participants; the number of unique participants with ASD is uncertain), with diverse designs and varying methodological quality were included, most of which were uncontrolled and had a high risk of bias. Across all four domains, the direction of effect supported aquatic intervention, and no study showed an effect favoring the comparator. The evidence was most concentrated and internally consistent for behavioral outcomes, for which all six controlled studies favored aquatic intervention, and five reported statistically significant results-although this tally reflects direction only and should not be equated with demonstrated effectiveness, whereas findings for social-emotional, emotion-related, and quality-of-life outcomes were positive in direction but mostly non-significant. Only one trial included an active land-based comparator, so a water-specific effect could not be distinguished. The available evidence suggests a consistent favorable direction across emotional and behavioral domains in children with ASD, but the evidence remains limited, heterogeneous, and at high risk of bias; sufficiently powered trials using active comparators and validated common outcome measures are needed. Systematic review registration: PROSPERO: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD420261390044, Identifier: CRD420261390044.