Explanation:

B4 is the ‘Brahmaputra Biodiversity and Biology Boat’.
Despite supporting considerable biodiversity, the Brahmaputra has not been studied as extensively as the Amazon.
The Centre plans to safeguard the fast-eroding Majuli Island using research carried out on floating ‘B4’ boat labs along the Brahmaputra River.
The project will “constantly monitor” the impact of various environmental and anthropological factors that affect the river and conduct research to mitigate the effects.
Majuli Island was once 1200 square kilometres but due to excessive erosion has since shrunk to under 500 square kilometres. Majuli Island is the biggest river island in the world toppling Marajo in Brazil.
The island is formed by the Brahmaputra River in the south and Subanisri River in the North. It is the 1st island district of the country.