Is Amelia Island in the Florida Keys?

The two get confused because both are Florida islands, and that is where the similarity ends.

Where Amelia Island actually is

The northeasternmost point of Florida: a barrier island in Nassau County, immediately south of the Georgia state line and about half an hour north of Jacksonville. It is a sand barrier island backed by salt marsh, on the same coastal system that runs up through the Georgia sea islands.

Why the difference shows up in the water

This matters more than the geography lesson suggests:

• The ocean is seasonal here. It runs 57.9°F in February and 84.6°F in August — a 27°F annual swing. The Keys barely move by comparison.
• The water is not turquoise. The shelf here is wide and shallow, the marsh drains tannins and sediment into it, and the tidal range is 6 to 7 feet. Expect green-brown Atlantic, not Caribbean blue.
• The tide does real work. A 6–7 ft range is large for Florida and it decides your beach day. In the Keys it is barely a foot.
• Winter is a real season. January afternoons average 64.3°F, and frost happens.

What you get instead

Thirteen miles of hard, walkable sand; a Victorian working port town with a downtown that has not been rebuilt as a resort strip; several thousand acres of tidal marsh behind the island; a nineteenth-century brick fort; and right whales calving offshore in winter. It is a different holiday, not a lesser one.

Our weather by month page has the full numbers, and water temperature by month explains the seasonal swing.