The large cluster of population in south asia is focused on the river basin, currently under threat from pollution and receding glaciers.

Ganges river basin      

Explanation:

Ganges river -

It is one of the popular river in the south asia , which originates from the mountain Himalayas , and flows entirely in the country India and then terminates at the Bay of Bengal .

The major threat to this river is the problem of pollution.

In Indian , the river is considered to be of huge spiritual importance , and hence , a lot of rituals are performed in the river , which in turns make the river dirty and polluted.

Hence , from the given information of the question,

The correct term is Ganges river basin.

1."lessen the worth of ."

2."increase the worth of."

3." beyond the worth of."

4."against the worth of ."