Abstract In this study we describe the seasonal effect of mountainous streams on crab’s population that how crab population are affected from change in climate. Seasonal variations can have a significant impact on crab populations. Factors such as temperature, water levels, and food availability can all play a role in determining the size and health of a crab population. A survey was carried out in the Balochistan province's Kachhi (Bolan) district between May 2019 and February 2020. Fresh water crab’s observations will be taken at the same site during (2019–2020) at the same time from around 12 AM to 02 PM on a monthly basis. One station is setup for sample collection for a period of one year, and once a week samples are collected. YSI 556 multi-probe sensors were used to measure the surface water quality parameters in-situ, such as pH, dissolved oxygen (DO), temperature (°C), and salinity (%) (mg -1). Station S1 is the deepest station, with an average depth of 0.48 0.31 m. Despite this, Station S2 is the shallowest, with an estimated mean depth of 0.33 0.11 m. The study region includes the District Kachhi (Bolan) in Balochistan's mountains. Gecarcinucidae and Potamidae families dominated the stream that was sampled. The total number of specimens obtained includes two species from the family Gecarcinucidae and three species from the family Potamidae. There were 142 freshwater crabs total, with Maydelliatelphusa lugubris accounting for 64% of the total (n=91).