Hindus don't bury their dead. They cremate them. Now there are polluting aspects to cremation but it can be done better than burial using proper incineration equipment. I have observed that such environmentally friendly cremation services are becoming more common in India even in smaller cities.

Not all Hindus cremate their dead. In fact a small minority do. In South India, burials are what you will see in nearly all the cases.

Only a certain castes cremate. Everybody else buries and yes river burial too is not common.

Lets talk of reckless dumping of human waste, industrial waste into rivers and lakes.

As a non-religious athiest hindu this is the first time I am hearing this, could you give some pointers. I would have expected it to go the other way (if at all), that is, only a small minority of hindu's do not cremate their dead.

In South India, we very rarely cremate.

Every village has a big "Rudrabhoomi". Cremation is a very upper caste thing.

Do yo have any citations that only a small minority of Hindus cremate their dead?

I also presume that the volume of bodies has increased in line with population, whilst the river volume has stayed constant (if not, in fact, decreased)

I'm going to make a modest proposal, but I wonder if there's enough caloric content in a body to make it worthwhile as feedstock in industrial aquaculture.

Nutrients preserved, value created, payments potentially made to the bereaved families. Everyone's a winner!