Turbidity: High turbidity means that the water is not very clean. Less turbidity means the water is cleaner. Turbidity is caused by suspended solids in water. These particles scatter light, making the water appear cloudy or cloudy. Turbidity can be seen with the naked eye. Turbidity is often used to estimate water quality. High turbidity means low water quality. According to the World Health Organization (WHO), the turbidity of drinking water should not exceed 5 NTU. Ideally, it should be less than 1 NTU. Optical devices are used to measure turbidity. With this device, particles hidden in water become visible. The particles can provide a hiding place for harmful microorganisms and thus protect them from the disinfection process. Suspended material can clog or damage a fish's gills, reduce its resistance to diseases, reduce its growth rate, affect the maturation of eggs and larvae, and affect fishing methods can affect the efficiency of the fishing method. Suspended particles provide adsorption medium for heavy metals such as mercury, chromium, lead, cadmium and many hazardous organic pollutants such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and many pesticides. The amount of available food is reduced because high turbidity increases the temperature of the water as suspended particles absorb more of the sun's heat. As a result, dissolved oxygen (DO) concentrations may decrease because warmer water carries less dissolved oxygen than colder water. Turbidity is measured by an instrument called a nephelometric turbidimeter, which expresses turbidity as NTU or TU. One TU is equivalent to 1 mg/litre silica in suspension .