Water Quality Assessment in the Northern Part of the Romanian Black Sea Coastal Area Using an Integrated Index

This study proposes and evaluates a specialized Recreational Water Quality Index (IR-WQI) designed to prioritize the bathers’ safety and comfort. Focusing on the Năvodari–Mamaia sector (2022–2024), the research investigates how different weighting configurations—prioritizing either microbiological safety or physicochemical stability—affect the accuracy of bathing water assessments. The IR-WQI was tested across four scenarios, comparing the sensitivity of a specialized pH-based “bather-comfort” penalty function against models that include salinity as a weighted constant. Results demonstrate high categorical stability, with 93.3% of monitoring sites maintaining their qualitative classification regardless of the weighting scheme. However, the inclusion of salinity was found to inflate quality scores, potentially masking fecal contamination at vulnerable sites. Scenario 1, which prioritizes microbiological indicators (60% weight) and incorporates a pH filter, provides a transparent and conservative diagnostic tool for coastal managers, thereby supporting sustainable tourism and informed decision-making for beach safety.