The
Ausa is a minor river some long that traverses part of northern
San Marino and
Emilia–Romagna in
Italy. The source of the river is
Monte Titano in central San Marino. The river flows northeast past
Serravalle and crosses the border into the Italian
province of Rimini close to
Dogana. The river continues flowing northeast and is channelled through storm drains at
Rimini before emptying into the
Adriatic Sea south of the mouth of the
Marecchia River. At above sea level, it is the lowest point of San Marino.