Complex sentence: A manatee nicknamed "Chessie" was rescued from the Chesapeake's chilly water in October 1994 and returned to Florida, but has revisited the Chesapeake several times since then, and photographed in the Patapsco River in 2010.
Split into simpler sentences: A manatee nicknamed "Chessie" was rescued from the Chesapeake's chilly water in October 1994 and returned to Florida. Manatees (or possibly the same manatee) have revisited the Chesapeake several times since then, and one was photographed in the Patapsco River in 2010.