How does this happen? What's the fix?

Elkton 130 inflatable kayak----after my most recent paddle there is water trapped in the inflatable pontoons, a good amount.
How does that even happen & how do I get it out?
All advise will be taken under consideration.

Looks like they offer a one year warranty. Sounds like defective valves or seams. Send it back.

Did you by chance leave it sitting out of the water at some point fully inflated on a hot day? That will expand the air inside and rupture a seam or valve attachment. I learned the hard way with my first kayak with inflatable sponsons that it doesn’t take long in the sun on dry land for one to expand and split. If you’ve caused hairline breaks or pinholes in seams you will get slow leaks that will replace some of the air in the tubes, especially if they have been hot and then are cooling because the boat was put back in the water. Air pressure will drop and allow more leakage.

Before your next step, inflate it as much as you can (with the water still in the bladders) and then submerge the inflated parts in water (pond, swimming pool or even bathtub and squeeze each bladder section to see if there are bubbles streaming out somewhere. If you do find leaks, the company may or may not offer you a warranty repair or replacement if they feel that the boat was not properly handled. But at that price they ought to offer some sort of customer service. Or you could just patch any holes you find with the patch kit that probably came with the boat and see what happens. If you have the quick deflate Boston type valves (the big ones with the smaller filling valves built into the caps) you should be able to inflate the boat and then open those and work some of the water towards the openings and out, then leave the caps off with it draped loosely somewhere that air can get inside for a few days.

You say “a good amount” of water. Be aware that if you inflate by mouth rather than by a pump or mechanical compressor, there is enough moisture in a human breath that you can get a little bit of condensation inside inflatables, but I would not call it “a good amount”.

Water can get inside the tubes also via the pump. I’m not saying this happened to you but it’s very important to check the pump before every inflating. Water can get into a pump surprisingly easily and then you just pump it into the tubes.