From Care Earth Trust, a Chennai, India based Technical Non-Governmental Organization founded in the year 2000:

PALLIKARANAI | Why dredging, deepening or dewatering the Marsh is a bad idea
The key to understanding the Pallikaranai marsh lies in its HYDROLOGY. The marsh acts like a SPONGE - meaning, it soaks up water during peak rainfall and releases it slowly during dry spells. Dredging will disturb this critical characteristic of the marsh.
The Pallikaranai marsh also plays an important role in GROUNDWATER recharge, especially for the South Chennai Aquifer that runs from the South of Adyar right upto Kovalam.
In light of these functions, dredging the Pallikaranai marsh will make #Chennai vulnerable to flooding during storm surges. This is a vulnerability the city of Chennai cannot afford to handle in its current state given the existing stresses on its wetlands.
It doesn't stop here! Dredging also carries other risks, including SEA WATER INTRUSION. It has the potential to make Chennai a semi-arid zone by drying out the landscape.
The marsh has a recorded 167 species of birds, 100 species of fish, 141 species of plants (including 29 species of native grasses). The bird migratory season coincides with post-monsoon months when the wetlands are full. The #wetlands of Chennai serve as nesting and breeding grounds for both transboundary and local migratory species
We urge the authorities to reconsider and withdraw the plan to dredge the #PallikaranaiMarsh. Let us work together in building evidence-based flood mitigation strategies for Chennai.