You would have to switch boats and docks at DTD. You would land at Marketplace dock from POR. Take an internal DTD Water Taxi from Marketplace dock to West Side dock. Take boat from West Side dock to either SSR or OKW, Here's the list of docks and boats handled at each:
Marketplace dock (east side DTD)
Disney's Port Orleans French Quarter and Riverside Resorts (Yellow Flag)
Downtown Disney Water Taxi (Red Flag)
Pleasure Island dock (center DTD)
Downtown Disney Water Taxi (Red Flag)
West Side dock
Disney's Saratoga Springs Resort & Spa and Treehouse Villas (Blue Flag)
Disney's Old Key West Resort (Green Flag)
Downtown Disney Water Taxi (Red Flag)