PORTLAND A last-minute flood of ballots slowed vote returns in a number of Oregon counties as the nation and state waited for the results from a hard-fought Senate race.

Beyond the sheer number of ballots, counties said a number of issues — creases in the ballots and their physical length among others — meant Oregonians would have to wait a little longer this year for some races to be declared.

The problems were notable if only because a number of races were too close to call based on the returns available Tuesday evening, including the U.S. Senate race and the secretary of state and treasurer races.

Election officials said generally the counting was running as smoothly as possible, given the number of voters and the limited amount of money to buy counting machines and hire staffers.

“The difference that we’re really talking about is curiosity and impatience,” said Rhys Scholes, a spokesman for Multnomah County Commission Chair Ted Wheeler. “When we’re deciding what’s the most cost-effective investment to make, you don’t gear up to have the fastest possible results on the largest possible election.”

Multnomah County, typically strong Democratic territory, was among the counties still processing a significant chunk of its votes Wednesday.

“It’s the large number of ballots returned in one day,” said Tim Scott, the county’s election director. “We got hit here at the end.”

This year, the county received 80,000 ballots on Nov. 4, the last day to turn them in. Four years ago, it received 67,000. Other counties saw a similar trend of Oregonians waiting longer to cast their vote.

Jill VanBuren, Benton County’s election administrator, said that she had two machines and two full-time staffer to work on returns. There’s no leeway in her budget to pick up more machines or hire more workers, she said, even if there were enough ballots to warrant it.

“All of the sudden we’ve got an election with a 90 percent return,” VanBuren said. But “it’s like everything else, there’s only so much money.”

The large returns, though, were only part of what has held some counties up.

Because of the number of measures up for vote this year, the ballots were physically longer, which meant the machines took more time to read them.

In Hood River County, voting machines misread creases that crossed bubbles on ballots. It appeared that some people had filled the bubbles of two candidates for the same office.

So, the election staff ended up painting over the bubbles the voters hadn’t filled in.

“It slowed us down quite a bit,” said Kim Haack, who oversees counting there. “It set us back probably a good three hours.”

A number of counties expected to finish up the counting by Wednesday evening. With votes still to be counted, statewide ballot-return rates are at 85 percent.