wet floor on driver's side of Accord

Hello everyone, I have a Honda Accord 1999 4 door LX. It only has
30,000 miles on it. I bought the car in Feb. 99, brand new.

In the last month I've had some water on the driver's side floor that
appears to be coming in from beneath the carpet. I think it's rain
related - I live in Portland OR, and we get tons of rain. I noticed it
when I detected the dismal smell of something dank and stagnant in the
interior. I checked the floors, and the driver's side is the only
place where there is moisture. I don't get standing water or anything,
but the wetness there seems abnormally high. I've removed the floor
mat (which was very wet underneath) and patted the carpet dry with
paper towels, and I've been keeping my eye on it. The carpet is drier
now, but it keeps on getting wet, and I'm pretty sure it's not from
water on my shoes when it's raining outside.

Anyone have any ideas? And if I were to take it in to a shop, should
it be a body shop or repair shop? As you probably can tell, I don't
know that much about cars.

Thank you for reading.

 

Do you have a sunroof?

 

I don't, thanks.

 

Look underneath the car, at the floorpan where the driver's feet go. Is the
big black rubber plug missing? It's about 2" in diameter.

 

Thanks, I will try that, although again i don't know much about cars.