Last fall's Bank Transfer Day and the social-media buzz around it translated to a bonanza for credit-union membership in the Pacific Northwest.

Washington's credit unions added 104,000 new members last year, 38,031 in the fourth quarter alone, according to the Northwest Credit Union Association, which is based in Federal Way. The 1.4 percent fourth-quarter growth in Washington was about three times higher than the growth seen nationwide.

Membership statewide zoomed to more than 2.83 million, the highest level since at least 1994, the earliest year for which federal data is readily available.

Total deposits reached nearly $28.4 billion, up from $26.8 billion a year earlier, according to data from the National Credit Union Administration.

The association chalked up the record gains to the awareness of credit unions generated by Occupy Wall Street and by National Bank Transfer Day, a Nov. 5 event in which an estimated 40,000 people nationwide moved their money into credit unions.

BECU, the biggest credit union in Washington, saw its membership grow by more than 10 percent and total deposits top $9 billion, up from $8.4 billion a year earlier.

While the largest credit unions saw healthy gains, less than half of Washington's credit unions saw membership increase over the previous year, an analysis of NCUA data shows.

Credit unions' deposits accounted for about one-fifth of all deposits in Washington state as of June 30.

It is possible to have too much of a good thing, however. If deposit growth exceeds loan demand, credit unions must find other investments that generate enough income to pay advertised interest rates, said John Annaloro, the association's president.

"More deposits doesn't represent a windfall," he said.

Credit unions could see their deposits tick up a little more from new accounts with state and local governments.

Under a new law signed by Gov. Chris Gregoire, these governments can deposit up to the insurance maximum — currently $250,000 per account — in state and federal-chartered credit unions.

Sanjay Bhatt: 206-464-3103 or sbhatt@seattletimes.com