The Tahoe Douglas Fire Protection District said the incident occurred Friday evening near Zephyr Cove, which is on the east side of the lake that straddles the California-Nevada border.
After the woman and the man went into the water, the boat with the children still aboard drifted into the middle of the lake where a fire district boat crew rescued the children, who were unhurt, the district said in a statement.
Rescue personnel were unable to revive the woman.
No identities were released. Additional information, including relationships between the people involved and ages of the children, wasn't immediately known.