Online real estate services company Zillow says in a new survey that the number of homeowners with a mortgage who are underwater has fallen below 20 percent for the first time since 2010.

“It is good news,” says Stan Humphries, Zillow’s chief economist, noting that the underwater number peaked at 31 percent in early 2012. “Coming down from the low 30 percent range back down to a lower number is great for the housing market.”

There is also not-so-great news about homeowners who are barely above water. George Mason University Real Estate Finance Professor Anthony Sanders says these homeowners don’t have enough equity built up to sell their houses at much of a profit, so it’s hard to  move.

“They look like everything’s ducky but it’s not… Even if they sell the house and pay all the fees to sell it,” Sanders says, “they wouldn’t be able to buy something – most likely – when they moved to another area of the country.”

Zillow says more than a third of homeowners with a mortgage are in this situation.