Lakes, ponds, and reservoirs are mostly stagnant waters with a very slow flow. This group contains mostly freshwater with few exceptions of mixed water and saltwater waterbodies. These waterbodies offer a rich habitat for various species and freshwater for consumption.

In cities around the globe, they reduce city temperatures, serve as recreational space, fishing grounds, and as a water management hotspot while preventing floods and purifying water. Stagnant water bodies in cities are especially sensitive to contamination from various sources.