The iron age bog people of Northern Europe were submerged in the oxygen-deprived bogs which helped with their preservation. This may have been an approach to burial reserved for sacrificial victims and may not have been used for the general population.

When you say interred do you mean completely submerged (which is difficult since the gas from decomp tends to make bodies float) or just put bodies in water as part of their funeral traditions?

One of the earliest archaeological sites in Florida, and by extension a very early site for human occupation in the Americas is the Windover Pond site.

The pond, really a peat bog, was used as a burial site over a period of ~1000 years, from 8000-7000 years ago. Occupation was not continuous, and clustering of the burials at the site suggests that burials were made "during at least five or six discrete episodes of short duration within the millennium of use." Whether it was the same people that continued to use the pond for burial over the milennium is uncertain, but Jerald T. Milanich writes that: "The possibility...is exciting."

Jerald T. Milanich, in Archaeology of Precolumbian Florida has this to say about the burials:

Each body was wrapped in fabric, which was then staked to the soft peat in or on the bottom of the pond, apparently to keep the body submerged (Doran and Dickel, 1988a:273, 276). We know that each individual was buried withing 48 hours after death because brain and other soft tissues, as well as proteins and mitochondrial DNA, are preserved.

168 bodies have been recovered at the site, although nearly half the pond and its contents remain excavated.

The peoples who used the pond also took the care of disabled individuals upon themselves:

One sixteen-year old buried at Windover died from a combination of poor health factors that included spina bifida, with a loss of sensory perception to the lower leg, and osteomyelitis, which ultimately resulted in the loss of one foot due to infection and bone deterioration (Doran and Dickel 1988a:277). Other pathological conditions also were observed in the burial population (Dickel and Doran 1989).

Milanich writes that children may have been valued due to the higher occurence of artifacts found with subadult rather than with adult burials, and he writes that "The importance of water to the early archaic people may be exhibited in their returning their dead to a pond for final burial."

All of the above taken from:

Milanich, Jerald T. Archaeology of Precolumbian Florida. University Press of Florida: 1994. Pp. 72-75

(its been a bit since i've done citations. forgive me!)