Husband John Blake said the shark was 1.8m long - "bigger than me".
"It was so sleek and fast. Gorgeous to look at." Mr Blake called police as he was concerned for the three surfers in the water near the shark.
Surfers were aware there were always sharks in the water. "It's just whether you see them or not," Mr Dickson said.
Senior Sergeant Steve Aitken confirmed police received the report, but said whatever it was, it had already moved on before police arrived.
Esplanade Surf School owner Steve Bennett believed the sighting was of a leopard seal.
"The police told us about 12.30pm that two people had seen a shark between St Kilda and Lawyers Head.
"People are used to seeing black seals and this was a lighter colour and about the size of a surfer.
"We see seals and sea lions all the time out here. They swim along the big channels to get fish."