Background <p>Assessing aquatic functional abilities is essential for designing effective interventions for children and adolescents who undergo aquatic activities and/or therapy. However, there is a lack of validated instruments in Spanish addressing this need. The Swimming with Independent Measure (SWIM) assesses functional performance in aquatic environments across typical and atypical development. This study aimed to cross-culturally adapt and to evaluate content equivalence and face validity of the SWIM for use with Spanish-speaking professionals working in aquatic environments with children and adolescents.</p> Method <p>A methodological study was conducted to perform the cross-cultural adaptation of the SWIM and evaluate its content equivalence and face validity. Cross-cultural adaptation followed Beaton’s six-phase methodology: translation, synthesis, back-translation, expert committee review, and pilot testing. Two translators and two back-translators performed the linguistic adaptation. A multidisciplinary expert committee (<i>n</i> = 5) evaluated content equivalence, and 20 professionals meeting predefined eligibility criteria participated in pilot testing. Content equivalence was assessed during the expert committee review, while face validity was evaluated during pilot testing.</p> Results <p>After two expert committee rounds, 83.6% of items were classified as conceptually equivalent and 16.4% as similar. Content equivalence indices improved from Ave-CVI = 0.93 to 1.00 and UA-CVI = 0.73 to 1.00. Pilot testing with 20 professionals confirmed adequate comprehensibility, requiring minor revisions to a few items. The final Spanish version showed adequate content equivalence and satisfactory face validity.</p> Conclusions <p>The Spanish version of the SWIM was cross-culturally adapted, demonstrating semantic, conceptual, idiomatic, and content equivalence with the original, and showed adequate face validity.</p>