RIO VISTA, Calif. (AP) – Everyone seems to have a suggestion to get two wayward whales lingering in the Sacramento River to swim 70 miles back to the Pacific Ocean.

One suggested towing life-sized replicas of orcas behind the whales to scare the recalcitrant mother humpback and her calf. Another proposed placing a giant magnet downriver, since humpbacks are thought to navigate by an internal compass that can sense magnetic north.

While rescuers have not tried the hundreds of suggestions they have received via e-mail – most of which are unfeasible – they acknowledge that they are running out of ideas.

“This is very much a work in progress,” said Trevor Spradlin, a marine mammal biologist with the National Oceanic and Atmospheric Administration working at the rescue scene.

Two weeks after the whales were first spotted in fresh water, the giant mammals’ behavior remained a mystery, even to scientists.

Biologists hastily drew up plans to spray the whales with fire hoses Friday after nearly a week of pipe-banging and whale recordings failed. Scientists used recordings to nudge a male humpback dubbed Humphrey out of the Sacramento-San Joaquin River Delta in 1985.

The pair got stranded after marking an apparent wrong turn earlier this month and heading upstream until they reached the Port of Sacramento and could go no farther. They turned around on their own Sunday, and swam some 20 miles downriver to the Rio Vista Bridge.

The central problem facing scientists trying to engineer new whale-herding techniques is that, while gentle coaxing has proved ineffective, they fear anything too forceful might make the situation worse. Nets pose a threat of entanglement, biologists said.

Any method that induces panic could separate the whales or send them fleeing, increasing the danger they could become stranded in the mud among the delta’s labyrinthine network of sloughs, they said.

During the week, rescuers grew concerned that some of the tactics they tried may have been too stressful for the duo. Some onlookers complained that scientists should stop interfering with the whales and allow them to follow their natural instincts.

The problem with that theory, according to veteran whale watchers, is that the humpbacks’ natural sense of direction has been thrown off severely by their 90-mile journey upriver.

“They’d probably like to just go north, but there’s no way they can do that,” said Ken Balcomb, executive director of the Center for Whale Research, who helped track Humphrey after he returned to the Pacific.

Mr. Balcomb gave poor marks to the current rescue effort, arguing that aggressive steps should have been taken to turn the whales around as soon as they were spotted. And, he said, the effort should have different leaders at the helm.

The most qualified whale herders in the world, Balcomb said, are Japanese whale hunters whose traditional pipe-banging technique known as “oikomi” has been passed down for more than 700 years.

Instead, at least a dozen federal, state and local agencies have been involved in the whale operation since the pair appeared.

As the mother and calf tarried near the Rio Vista Bridge, their health deteriorated.

“The loss of any single animal would be bad. The loss of a breeding animal and her calf would be a substantial biological punch,” said Brian Gorman, a NOAA spokesman. “To ignore the plight of such iconic animals as humpback whales in such a public place would be unthinkable.”