**3. Results**

The physicochemical characteristics of the rainwater harvesting ponds are given in Figure 2. The water temperature ranged between 18–30 ◦C. The pH was measured between 6.5 and 9.2. A high variation was observed in the conductivity values, in which the highest conductivity was measured in S10 (890 μS/cm) and the lowest was recorded as 112 μS/cm in S14. While TP was measured below 100 μg/L in most of the ponds, the highest value was measured in S11 as 237.5 μg/L. Total nitrogen was detected in the range of 0.7–1.9 mg/L in which the maximum value was detected in S16 followed by S10 (1.6 mg/L). Furthermore, a high variation was observed in the chlorophyll-*a* concentration in which the highest level was detected in S10 as 82 μg/L. Microcystin was found in S16 as 13.80 μg/L.

Cyanobacteria were detected in three samples (S10, S11, and S16) out of 17 ponds (Figure 3A). In two of these ponds, cyanobacterial blooms were observed, with Cyanobacteria comprising 82% of the community in S16 and 72% in S10. In detail, *Microcystis* sp. was responsible for the bloom in S16 while *Aphanizomenon* sp. and *Cuspidothrix issatschenkoi* were in S10 (Figure 3B).

**Figure 2.** Physicochemical characteristics of the rainwater harvesting ponds during the summer 2022 (**A**) Total Phosphorous, (**B**) Total Nitrogen, (**C**) Chlorophyll-*<sup>a</sup>*, (**D**) pH, (**E**) Temperature, (**F**) Conductivity.

**Figure 3.** Phytoplankton community composition (**A**) phylum level, (**B**) genus level.
