Around 9:45 a.m., the owner of a 27-foot fishing vessel called for help for his 51-year-old wife, who was losing consciousness, according to Coast Guard Petty Officer Adam Stanton.
A Coast Guard crew from Station Rio Vista was dispatched to the fishing boat in the Sacramento Delta about 2 miles south of Rio Vista, Stanton said.
The spokesman said crewmembers arriving on the scene found both the husband and wife unconscious aboard the fishing vessel and quickly evacuated the pair.
The crew anchored the fishing boat and took the two victims to Station Rio Vista.
Stanton said medical personnel treated the couple for possible carbon monoxide poisoning, and the pair regained consciousness after receiving oxygen.
"Giving them oxygen right away and the fast response were key," the officer said.
A Sacramento Police Department hazardous materials team is investigating whether the boat contained carbon monoxide.
Carbon monoxide is odorless, colorless, tasteless gas produced from carbon-like fuel such as gasoline, propane or charcoal.
The toxic gas can accumulate in and around boats for a variety of reasons, including blocked exhaust outlets, inadequately ventilated canvas boat coverings or from another vessel's exhaust, according to the Coast Guard's Boating Safety Resource Center.