<P> As there is a maze of many river branches, the area is difficult to pass . Most islands are only connected with the mainland by simple wooden ferryboats . Bridges are rare . Some islands are not yet connected to the electric grid, so island residents tend to use solar cells for a bit of electric supply . </P> <P> Arsenic is a naturally occurring substance in the Ganga Delta that has detrimental affects on health, and may enter the food chain, especially in key crops such as rice . </P> <P> The Ganges Delta lies mostly in the tropical wet climate zone, and receives between 1,500 to 2,000 mm (59 to 79 in) of rainfall each year in the western part, and 2,000 to 3,000 mm (79 to 118 in) in the eastern part. . Hot, dry summers and cool, dry winters make the climate suitable for agriculture . </P> <P> In November 1970, the deadliest tropical cyclone of the twentieth century hit the Ganges Delta region . The 1970 Bhola cyclone killed 500,000 people (official death toll), with another 100,000 missing . The Guinness Book of World Records estimated the total loss of human life from the Bhola cyclone at 1,000,000 . </P>

Name the tidal forests of the ganges delta