Scientists are using a new approach to coax two wayward humpback whales to leave the Delta and return to sea. Authorities said the whales -- a mother named Delta and a calf called Dawn -- are showing increasing signs of distress as they linger in fresh water near Rio Vista.
The whales, which normally roam the Pacific, have received intense interest from scientists and the public since they were spotted in waters off Rio Vista on Mother's Day.
The animals are currently about 70 miles inland and officials are worried conditions may become more dangerous as hordes of boaters take to the water over the upcoming Memorial Day weekend.
Experts planned Wednesday to use different whale sounds to lure or drive the animals away. A recording of whales feeding in Monterey Bay will be used along with another recording of manmade sounds not found in nature.
Plans also call for playing the sounds of a killer whale attacking a mother whale and calf in hopes of scaring the whales away.
So far, other whale sounds have been played, but did not have much effect. Officials have also been banging on boat-mounted pipes partially submerged in the water to create unpleasant noises intended to get the animals to leave.
Rio Vista is expected to be a tourist hot spot over the weekend. The town is home to about 7,500 people, but it will swell by thousands over the weekend as people arrive to recreate and see the whales.
Jon Copley of the Coast Guard urged recreational boaters to keep an eye out for the whales. Officials will be enforcing a 500-yard safety zone around the animals.
Meanwhile, marine mammal experts are investigating the discovery of a dead whale in San Francisco Bay. The animal was found off the coast of Angel Island Wednesday night. It is not one of the whales seen this week near Rio Vista, officials said.
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