DENVER — Among the many oddities that have arisen from marijuana legalization in Washington and Colorado is this: It can be easier to get through airport security with a bag of weed than a bottle of water.

At Washington’s airports, including Seattle-Tacoma International, there’s nothing police can do to prevent travelers from flying with pot in their carry-on or checked luggage, provided it doesn’t exceed the state legal limit of one ounce. Instead, airport officials say, officers simply recommend that travelers leave it in their cars, toss it or have a friend pick it up.

But in Colorado, where the legal pot law gives property owners more authority to restrict the drug, some airports have banned marijuana possession and enacted penalties, including fines as high as $2,500 and a jail stint at the airport in Colorado Springs.

“Carrying marijuana in a civilian aircraft is illegal under federal regulations. That’s why we implemented the rule, to prevent marijuana from reaching a civilian aircraft,” said airport spokeswoman Kim Melchor, adding that the airport has yet to levy a fine and that a drop-box where travelers can toss excess weed hasn’t been used.

The situation underscores the difficulty officials in both states have as they try to prevent pot from leaving their borders — one of several conditions the Department of Justice imposed when it allowed the legal pot experiments to proceed.

An attorney with Smart Colorado, which opposed legalization, worried about tourists transporting tiny, concentrated products, such as hardened hash oil that has enough THC, pot’s primary psychoactive chemical, for hundreds of uses.

“For the size of a traveler’s shampoo bottle, you can serve an entire urban high school and get them stoned,” Rachel O’Bryan said.

Voters in the two states approved legalizing marijuana for adults over 21 in 2012, but the laws don’t allow people to take pot out of state. Federal law prohibits marijuana possession, on a plane or anywhere else. Anyone who touched down in the other 48 states where marijuana is illegal would also be violating state law.

While the Justice Department said it wanted the states to keep the legal weed in state, there’s been little to keep people from trying to bring back souvenirs from the legal-pot states.

The Transportation Security Administration makes travelers empty their water bottles, but when agents encounter personal amounts of marijuana at security checkpoints, they typically don’t call the DEA or FBI. Federal prosecutors don’t waste their time on such small potatoes. An agency spokesman said TSA’s focus is on terrorism and threats to the aircraft and passengers.

TSA agents normally hand over pot cases to local law enforcement officers, who have little recourse in Colorado and Washington. At Sea-Tac, they rely on a “totality of the circumstances” test to decide whether to make an arrest or investigate further, Port of Seattle spokesman Perry Cooper said: Is the passenger combative or assaultive, or carrying vast amounts of cash?

Detention might be warranted for some of those things, but not for the pot itself, he noted.

Airports say there have been few incidents where passengers have been stopped carrying marijuana. The Port of Denver banned pot at Denver International, with fines of up to $999. No one’s been fined yet.

At the urging of Pitkin County Sheriff Joe DiSalvo, Aspen’s airport is installing an “amnesty box” where travelers can drop any leftover weed before taking to the skies. In the few cases where travelers have been caught trying to take pot on a plane, they have received polite reprimands and no legal consequences.

“How do we invite people here, tell them they can use a product and then prosecute them when they try to leave the state?” he asked.

His office has confiscated marijuana edibles from several travelers at the Aspen airport — after obtaining voluntary releases of the property — but has not taken legal action against them.

Travelers were caught taking as much as five pounds of pot-infused candies and oils, he said. But the Colorado initiative allows people to carry up to one ounce of THC. DiSalvo said there probably was not that amount of THC in even the largest load.

Jeffrey Gard, a Boulder attorney who represents marijuana users and sellers, said there’s no reason for Colorado airports to worry about people boarding a plane with pot. “By law, it’s no different than bringing a flask or a pack of cigarettes,” he said. “As tourists come here and do dumb things you’re going to see more of these things happen.”

Still, Gard advises clients not to board planes with pot. The risk, he and other marijuana advocates say, is too great.

Sean McAllister, a lawyer who is on the board of the Colorado chapter of NORML, a pot legalization group, said that medical marijuana patients used to be allowed to fly with their medication to other states with similar laws. But Denver’s airport ban on pot, which went into effect on Jan. 1, now means those patients may get their legal medication trashed, he said.

“The law’s getting looser in Colorado, and they’re getting stricter,” McAllister complained.

Airports elsewhere say they aren’t bracing for an influx of travelers carrying marijuana from Colorado and Washington.

“Law enforcement officers in Texas enforce the laws of Texas, and it’s incumbent on people from Colorado to know the laws in places where they’re going,” said David Magana, a spokesman for Dallas-Fort Worth International Airport.