Each quarter, RealtyTrac releases its "Home Equity and Underwater Report."

According to RealtyTrac's data, "9.1 million U.S. residential properties were seriously underwater." Mortgages that are "seriously underwater" exceed a property's value by at least 25 percent. They also account for 17.2 percent of all properties with a mortgage.

That number decreased slightly (0.2 percent) in the second quarter. In the second quarter of 2012, there were 12.8 million properties that were "seriously underwater" -- 29 percent of all homes with a mortgage.

The improvement in underwater mortgages may be coming to an end. Recently, home-price appreciation has tailed off and if interest rates rise, all bets are off. At the same time, the number of homes that are "seriously underwater, many of which have deep negative equity," remains substantial. RealtyTrac notes that the average loan-to-value ratio for these homes was 133 percent.

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Our chart of the day shows the states with the highest percentage of residential properties seriously underwater.

To contact the author on this story:
Barry L Ritholtz at britholtz3@bloomberg.net