is a part of the eastern Himalayas mountain range. In this region is Sandakfu, which, at , is the highest peak in the state. The narrow Terai region separates the hills from the North Bengal plains, which in turn transitions into the Ganges delta towards the south. The Rarh region intervenes between the Ganges delta in the east and the western plateau and high lands. A small coastal region is in the extreme south, while the Sundarbans mangrove forests form a geographical landmark at the Ganges delta. The main river in West Bengal is the Ganges, which divides into two branches. One branch enters Bangladesh as the Padma, or Pôdda, while the other flows through West Bengal as the Bhagirathi River and Hooghly River. The Farakka barrage over the Ganges feeds the Hooghly branch of the river by a feeder canal. Its water flow management has been a source of lingering dispute between India and Bangladesh. The Teesta, Torsa, Jaldhaka and Mahananda rivers are in the northern hilly region. The western plateau region has rivers like the Damodar, Ajay and Kangsabati. The Ganges delta and the Sundarbans area have numerous rivers and creeks. Pollution of the Ganges from indiscriminate waste dumped into the river is a major problem. Damodar, another tributary of the Ganges and once known as the "Sorrow of Bengal" (due to its frequent floods), has several dams under the Damodar Valley Project. At least nine districts in the state suffer from arsenic contamination of groundwater, and as of 2017 an estimated 1.04crore people were afflicted by arsenic poisoning. West Bengal's climate varies from tropical savanna in the southern portions to humid subtropical in the north. The main seasons are summer, the rainy season, a short autumn and winter. While the summer in the delta region is noted for excessive humidity, the western highlands experience a dry summer like northern India. The highest daytime temperatures range from to . At night, a cool southerly breeze carries moisture from the Bay of Bengal. In early summer, brief squalls and thunderstorms known as Kalbaisakhi, or Nor'westers, often occur. West Bengal receives the Bay of Bengal branch of the Indian Ocean monsoon that moves in a southeast to northwest direction. Monsoons bring rain to the whole state from June to September. Heavy rainfall of above is observed in the Darjeeling, Jalpaiguri, and Cooch Behar district. During the arrival of the monsoons,