<p>Liquid crystal elastomers (LCEs) are increasingly used as artificial muscles to power a variety of soft robots. Although LCEs exhibit similar deformation upon stimulation in both air and water, experiments reveal that their mechanical properties are significantly compromised after soaking in water, which prohibits long-term underwater usage. In this work, we systematically investigate how and why water affects the mechanical properties of LCEs, considering two commonly used liquid crystal monomers: C6M and C3M. Through soaking and dehydration experiments combined with mechanical testing, molecular dynamics simulations, and Fourier-transform infrared spectroscopy, we reveal that water induces both swelling and chemical degradation that result in notably reduced mechanical strength. Furthermore, we try different strategies to prevent such strength reduction, including tuning oxygen content, varying crosslink density, and eliminating oxygen-containing crosslinkers, but achieve limited success, as swelling and chemical degradation persist. Despite these unsuccessful attempts, we demonstrate that encapsulating LCEs with a butyl rubber-based coating presents an effective waterproofing strategy, significantly preventing the mechanical strength reduction. This study provides a fundamental understanding of the mechanical properties of soaked LCEs and thus provides practical guidelines for developing durable LCE-powered robots for underwater environments.</p>