BOSTON – The worst shellfishing season in decades may have a sequel this summer, thanks to recent record rains coupled with wind and water conditions similar to what fed last year’s ruinous red tide.

Early this week, rainwater runoff forced the state to shut down shellfish beds from the New Hampshire border to Cape Cod and Buzzards Bay. At the same time, the state enacted a red tide closure of shellfish beds from the New Hampshire border to Deer Island in Boston Harbor.

Scientists said Wednesday the recent weather has created conditions similar to what allowed last year’s red tide to spread.

“Whether it’s going to be … as big and lasting as last year, there’s no way to tell,” said Michael Hickey, the state’s chief shellfish biologist.

The toxic algae cells are absorbed by shellfish, making them hazardous and even deadly to eat. The 2005 red tide bloom closed the state’s shellfish beds for months during the peak spring and summer season and caused $50 million in losses to tourism and fishing industries.

“It’s very frustrating, but you know what it is, it’s part of a clammer’s life,” said John Grundstrom, a fifth-generation shellfisherman from Rowley. “If you depend on it, you’re a fool.”

This month’s rains created runoff from flooded rivers, roads and overwhelmed sewer systems that carry waste and bacteria, which pollute shellfish beds, Hickey said. The swelled Merrimack River is dumping so much water into the ocean it’s probably affecting water quality down to Boston, he said.

The rain has caused similar problems in Maine, where flooding has forced the closure of clam flats from Cape Small in Phippsburg to the New Hampshire border.

“This could be a pollution problem for several weeks,” said Darcie Couture, director of biotoxin monitoring for the Department of Marine Resources. Red tide isn’t yet a big problem, she said, adding more testing will be conducted Friday.

It’s impossible to say how long the rain-caused closures could last, because the sources of pollution and remedies differ in different ecological areas. Hickey said the red tide closure may outlast any rain-caused shutdowns, anyway.

Don Anderson, a red tide expert from the Woods Hole Oceanographic Institution in Falmouth, said the unique conditions that fed the wild spread of last year’s red tide have recurred.