be up to (one's) knees in (something)

1. Literally, to have one's legs submerged in some substance to the height of one's knees. We were up to our knees in filthy muck as we made our way through the marsh. Get over here with those buckets! I'm already up to my knees in water! Man, the hurricane really tore apart this whole area. We're up to our knees in debris here.

2. To have an abundance or excess of something. A: "Will you buy this old TV off of me?" B: "No thanks. We're up to our knees in these old units as it is." You're up to your knees in books—why do you keep buying more? I'm still unpacking, so I'm up to my knees in boxes.

3. To be very busy with or deeply engrossed in something. I'd love to come for a pint, but I'm up to my knees in work at the moment. Don't bother her right now, she's up to her knees in lesson planning. What was that? Sorry, I'm up to my knees in paperwork because one of my guys got hurt at the construction site today.