More homeowners are slipping below the waterline.

About 125,000 homes in the Baltimore region were worth less than what their owners owed on the mortgages at the end of last year, up from nearly 120,000 last summer, according to estimates from real estate data firm CoreLogic. All told, close to 20 percent of borrowers are upside down on their mortgages, the company said.

The underwater phenomenon grew nationally as well, engulfing an additional 400,000 homes and inching up to nearly 23 percent of all residential properties with a mortgage. (The national share is high in part because big states such as California and Florida are in particularly rough shape.)

Declines in home prices are the issue. If you're almost underwater, the progress you're making by paying down your principal might not be enough to keep you on the right side of the loan-to-value equation while values drop.

Speaking of which: 33,000 Baltimore-area homeowners were close to the tipping point at the end of last year, CoreLogic says. That's 5 percent of homes with mortgages.

Industry watchers care about these measures because borrowers far underwater are potential "walkaway" risks -- meaning they can afford to pay the mortgage but decide it no longer makes financial sense.

Even without strategic default, there's a market impact: Those in the negative-equity crowd are stuck where they are, unless they bring money to the settlement table, convince their bank to approve a short sale or turn the home into a rental. (More on that in Sunday's paper.)

CoreLogic ranked the states by their share of negative equity plus "near negative equity," and Maryland remains high on the list -- No. 9, with nearly 30 percent of loans. But in the could-be-worse category, it's still nowhere near the top states: Nevada (almost 66 percent), Arizona (53 percent) and Florida (48 percent).

Are you underwater? Does it make a difference?