Swimming pools can act as reservoirs of pathogenic microorganisms when poorly maintained. This study assessed the microbiological and physicochemical quality of seven outdoor public swimming pools in Nnewi North, Anambra State, Nigeria, before use and after use by bathers on weekends, Saturdays and Sundays. Water samples were aseptically collected between September and November 2024 and analyzed using standard methods. Heterotrophic bacterial counts increased from 6.35 × 10⁴ CFU/ml before use to 6.51 × 10⁴ cfu/ml after use, while fungal counts ranged from 0–2.13 × 10⁵ cfu/mL before and 0–3.0 × 10⁵ cfu/mL after use. The mean±SD total heterotrophic bacterial counts (THBC) before use (49.5714±21.8210) and after use (50.8571±22.4305), and the mean total heterotrophic fungal counts (THFC) before use (13.0476±11.7195) and after use (14.8571±13.5288) were considered statistically significant at p = 0.05. Bacterial isolates rose from 242 before use to 378 after use, with increased occurrence of Escherichia coli (11.9%), Enterobacter intermedius (11.1%), Citrobacter freundii (10.6%), and Klebsiella pneumoniae (10.1%). Fungal isolates also increased from 40 before use to 70 after use, predominantly Penicillium (28.6%), Curvularia (24.3%), and Aspergillus (21.4) species. Most Probable Number (MPN) index/100 ml for total coliforms (<3–93 MPN/100 ml) and fecal coliforms (<3–12 MPN/100 ml) exceeded WHO/EPA limits after use. Mean±SD physicochemical parameters before and after use by bathers indicated deteriorating water quality of the swimming pools, with reduced pH (5.56±1.23–5.32±1.11), residual chlorine (0.59±0.82–0.52±0.739 mg/L), salinity (438.64±178.92–231.42±104.71), and calcium hardness (199.670±181.80–78.51±73.31 mg/L) alongside increased temperature (26.18±0.69–28.31±0.64°C), turbidity (9.91±04.58–14.83±2.47 NTU), nitrate (0.31±0.20–1.12±0.99 µg/L), alkalinity (92.83±60.75–160.00±81.86 mg/L), and ammonia (0.66±0.03–0.77±0.74 mg/L) after use by bathers. The mean physicochemical parameters before and after use by bathers were considered statistically significant at p = 0.05. Bacterial isolates showed high susceptibility to fluoroquinolones but resistance to β-lactam antibiotics, while fungi exhibited notable antifungal resistance, particularly against fluconazole and griseofulvin. Most pools in this study failed to meet recommended standards, posing public health risks and highlighting the need for improved monitoring and maintenance.