Hundreds of city residents thronged Mahim beach, following reports of sea water turning sweet even as Chief Minister Vilasrao Deshmukh and government agencies cautioned them on Saturday against drinking water from the creek.

Even as people began coming to the beach in large numbers since Friday night to taste the 'miracle', government agencies including the Brihanmumbai Municipal Corporation tested the water samples and warned it was 'unfit' for drinking.

"The samples show that the water is highly unfit to drink and contains very low levels of salt, which could be the reason for it tasting sweet. We would advise people not to drink the water," BMC source told PTI.

Chief Minister Vilasrao Deshmukh, too, has appealed to the people not to drink the water as it could contain 'dangerous substances'.

Explaining the phenomenon, the Maharashtra Pollution Control Board has said it could be an upsurge of ground water, which is caused due to heavy rainfall in the area.

"Due to heavy rainfall in the area, the ground water gets fully charged and may exert excess pressure. This can cause fine cracks in the rocky bottom through which ground water tends to come out," Dilip Boralkar, member secretary of the MPCB said.

"Fresh water being lighter than sea water will float on the surface and may taste relatively sweeter. Normally, seawater is low in salinity during the monsoon because of the continuous rainfall in the area. This year we have had heavy rains in Mumbai ground water being fully charged may be the cause," he added.