Lonely Planet: Kerala, India: Reality Check ...backwater mentality...
Although the backwaters have become an important tourist attraction, they are also under severe threat from population growth and industrial and agricultural development. Kerala has 29 major lakes on the backwater system, seven of which drain into the sea. It's estimated that the area of these lakes has fallen from 440 sq km in 1968 to less than 350 sq km today, due to legal and illegal land reclamation projects and urban development.

Ecological damage has included pollution, the extinction of mangroves, crocodiles and migratory fish, and the destruction of oyster beds. Many migratory birds no longer visit the backwaters, and destructive fishing, using dynamite, poison and very fine nets, has also caused great damage. To the casual eye, the most visible danger is the unhindered spread of water hyacinth which clogs many stretches of canal and causes great difficulties for the boat operators.