This study aimed to develop and examine the quality of a domain-specific instrument for creative thinking skills on dynamic fluid topics. The instrument was designed as an open-ended essay test based on four creative-thinking indicators: fluency, flexibility, originality, and elaboration. These indicators were contextualized in terms of the continuity principle, Bernoulli's law, and its applications. The development procedure included a literature review, construct specification, blueprint and rubric development, expert validation, revision, empirical try-out, and instrument quality analysis. Content validation involved six experts, while the empirical try-out involved 66 grade XI science students. The content validity analysis yielded an S-CVI/Ave of 0.991 and an S-CVI/UA of 0.946. All seven items were empirically valid, with item-total correlations ranging from 0.469 to 0.736. The internal consistency coefficient, measured using Cronbach's alpha, was 0.759. Inter-rater reliability for four essay items ranged from 0.688 to 0.844 (Cohen's kappa). Item difficulty analysis indicated four easy items, two moderate items, and one difficult item. These findings indicate that the developed instrument has adequate validity, reliability, scoring consistency, and item characteristics for assessing students' creative thinking skills in dynamic fluids, particularly in physics learning that emphasizes problem solving and scientific idea development.