Assessment of Water Quality and Antimicrobial Activity of Bloom-forming Algae from Waddepally Reservoir

Abstract

This study assessed water quality, algal bloom dynamics and antibacterial activity of bloom-forming algae from Waddepally Reservoir, Hanamkonda, during November 2021 to October 2025. Monthly water samples were collected from selected sites and analysed for physicochemical characteristics, phytoplankton abundance and seasonal changes in optical properties. Algal biomass and light transmission were examined using a Carolina spectroscopy chamber with red, green and blue filters and an RGB colour detector. Phytoplankton samples were identified microscopically, quantified using a Sedgwick-Rafter counting cell and interpreted using Nygaard’s phytoplankton indices. Selected algal isolates were cultured in Chu-10 and BG-11 media under controlled light and temperature conditions, and crude extracts were tested against five bacterial strains using the agar well diffusion method. The reservoir showed pH values of 6.0-8.6, water temperature of 22-30 °C, turbidity of 0.01-6.00 NTU and transparency of 24-123 cm. Dissolved oxygen remained comparatively high (6.3-9.8 mg/L), while BOD ranged from 2.6 to 20.5 mg/L and COD from 0.32 to 0.94 mg/L. Heavy metals, including chromium, cobalt, lead, mercury and zinc, were not detected. Nygaard’s indices indicated eutrophic conditions, particularly through the Chlorophycean, Euglenophycean and Compound indices. Spectroscopic readings showed seasonal variation in light transmission, with dense algal mat formation during April and May. Antibacterial screening indicated solvent-dependent activity. Acetone extracts showed the highest inhibition zone against Micrococcus luteus (14.33 mm), while methanol extracts inhibited Staphylococcus aureus (12.22 mm) and Salmonella typhi (11.33 mm). These findings indicate that algal communities can support reservoir water-quality monitoring and that selected bloom-forming algae possess measurable antibacterial activity.