MINNEAPOLIS (WCCO) — Standing shoulder-to-shoulder spectators soaked up one last look. They came down to the Upper St. Anthony Falls Lock before midnight Tuesday, when the 53-year old river gateway closes for good.

“The reason this is being closed down is because it’s the one sure way to keep these carp from spreading into our beautiful lakes and fishing areas of northern Minnesota,” Sen. Amy Klobuchar said.

READ MORE: COVID In Minnesota: 2,424 Cases, 3 Deaths Reported Friday

Sen. Klobuchar sponsored the legislation, which was signed into law in June 2014. It required the lock’s closure within one year in an effort to prevent the further spread of invasive silver and big head carp into the Mississippi River watershed.

“These fish will take over,” out of town visitor Kathy Becker said.

Even tourists like Becker understand how the jumping, voracious invaders are knocking on the door. Just last week it was announced that five of the big head carp were caught in the St. Croix River near Stillwater.

“I think it’s hugely important you all acted so quickly because there are so many examples all around the globe,” Becker said.

Had the invasive carp been able to navigate upstream of St. Anthony Falls, it could spell catastrophe for Minnesota sport fishing. That’s because a breach at the Coon Rapids dam, which was recently fortified, could give the carp a pathway into Minnesota’s north central lake country.

Though initially constructed for commerce the lock closing will impact pleasure boats as well.

READ MORE: Man Fatally Shot On Downtown St. Paul LRT Platform; 2 Others Killed In Separate Shootings

“They grew up doing this and their kids and grandkids won’t be able to enjoy it,” Robert Shell said.

Since only April of 2015, 195 barges have carried some 293,000 tons of sand, cement, salt and scrap steel up and down river through St. Anthony Falls. That traffic is now forced to shift onto trucks from ports downstream.

That amount of barge commodities would require the equivalent of 11,300 semi-trucks to transport.

(credit: CBS)

(credit: CBS)

By mid-afternoon Tuesday, a flotilla of kayakers passed through one final time. WCCO-TV Reporter Kylie Bearse was among them, soaking in the cavernous view as the huge steel doors swing open to the lazy river below.

For longtime lockmaster Mike DeRusha, it’s the end of an era.

MORE NEWS: Jackie Young Scores 25 For Aces In 93-87 Win Over Lynx

“The Becky Sue just went up to grab the last two barges that are above us, when they go through it’s in all likelihood the last commercial lockage we’ll ever have here,” DeRusha said.