Crews are continuing to monitor the Boise River in Garden City where a large tree fell into the water last week, causing the water to back up and flow over the banks.

Garden City Mayor John Evans told KTVB they are keeping a close eye on the situation since there is a chance the tree could break free and come downstream toward the Glenwood Bridge, which would pose an even bigger issue.

"It has probably 10-foot root ball that is not dispersing, and that root ball as the water pushes up against it, the water elevation behind the root ball raises and then it wants to move laterally,” Evans said. “And if that root ball is near the bank then it pushes water over the bank."

That’s what happened Friday when the tree fell into the river and got lodged, causing flooding near several businesses and a trailer park. Since then, the tree has moved a couple of blocks downstream.

As of Monday, it’s not causing a backup, but the mayor said they aren’t resting easy just yet. He said Garden City, along with the Ada County Highway District, are continuing to monitor the tree. As far as removing it, that isn’t as easy as you might think.

"The root ball is the problem and you have to be careful about how you deal with the root ball,” Evans said. “One, it's extremely heavy, so number two, because of the water saturations at the banks, you have to be careful about getting heavy equipment on the banks."

Crews are also checking bridges and other infrastructure to make sure those are holding up, and considering the possibility other trees could fall in the river as well.

“There's a place on the river by Linder Road, and actually I just received an email that there's a tree that's fallen near Veteran’s pond," Nicole Dubois, a spokeswoman for ACHD said.

"We just have to really be vigilant,” Mayor Evans said. “We are watching the banks, between the city of Garden City, the Ada County Highway District, that river bank has eyes on it at key locations 24 hours a day."