Taylor Swift -- Obsessed Fan ARRESTED for Swimming to Singer's Beach Pad

An obsessed Taylor Swift fan was arrested near the singer's Rhode Island beach home early this morning after allegedly SWIMMING up to her pad ... TMZ has learned.

Law enforcement tells us ... a 22-year-old male from the Chicago area was taken into custody for trespassing after he admitted to swimming up to the beach in front of Swift's home around 2 AM.

Here's the back story -- around 2:20 AM, cops spotted the man getting out of the ocean, around 1 mile from Swift's home.

Cops approached the guy and asked him what he was doing in the water -- and the man allegedly told police he had just completed a swim, in which he intended to meet Taylor.

Sources say ... the man told cops he swam all the way to Swift's beach, but saw her security team ... and decided to swim back to where he came from (roughly 2 miles round trip in cold water).

The man was hauled to a nearby police station where he was booked for trespassing. He's still in custody.

We spoke to the Westerly Police Dept. which tells us, "There is a zero tolerance policy for trespassers." The cops say they have already met with Taylor's security to discuss the matter.