According to NSW Government agency, Manly Hydraulics Laboratory (MHL), who has six ocean-monitoring buoys located along the NSW coast, the sea temperature off Crowdy Head has dropped from 22.85 degrees on Friday, December 27 to 15.7 degrees today, January 1.

Currently it is the coldest MHL-monitored location in the State, with Eden on the NSW Far South Coast the next coldest at 18.6 degrees.

MidCoast lifeguard supervisor, Warren Keegan, said the sharp drop had been registered by beachgoers and lifeguards alike.

"It's been quite a noticeable drop in sea temperature the last couple of days," Mr Keegan said.

He believed the icy conditions hadn't so much impacted the amount of people attending patrolled beaches, but it'd definitely influenced how much time people were spending in the water.

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Luckily, lifeguards hadn't had to respond to any cases of cold exposure yet.

"Most people are sensible about it," Mr Keegan said.

"It would more be in the case of a rescue situation with a rock fisherman or something that it'd become a concern."

Mr Keegan pointed to the strong nor-easterly winds experienced along the coast in recent days as a likely contributor to the temperature drop.

Meteorologist, Ben Matson, explains the link between nor-east winds and a drop in sea temperatures on Australian surf forecasting site Swellnet.

He says the process is called 'Ekman Transport' and refers to an upwelling effect that occurs during certain weather patterns.

"When the wind blows along the ocean's surface, the effects of the Coriolis force diverts the top layer of water to the left in the southern hemisphere (while in the northern hemisphere, the top layer of water is diverted to the right)," Matson explains.

"Therefore, a nor-easterly wind blowing along the coast pushes the top layer of water out into the Tasman Sea. As this water needs to be replaced, an 'upwelling' effect draws in cooler (and usually nutrient-rich) water from below.

"It usually takes a couple of days of nor-easters to see any noticeable change, and you'll also find that certain parts of the coastline tend to react more than others - usually due to the presence of underwater ridges and canyons that amplify the upwelling effect."

The antidote to cold sea surface temperatures usually takes the form of a southerly wind change, but with none predicted along the Mid Coast over the next seven days, the water is likely to remain icy.

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