The Department of Environmental Conservation says it was called Friday about an oil sheen in the water around the Marshall Islands-based South Wind, docked at Grimmel Industries in the Port of Rensselaer.
Investigators say the ship's captain described a buildup of pressure from the engine's waste oil tanks, which backed up through the vent pipes and caused oil to spill onto the deck.
They say the crew collected oil and poured at least 20 gallons into its drain ports, which discharged into the river.
The captain and South Wind Shipping Corp. were cited for violations.
The DEC says the oil dissipated in outgoing tide and had minimal environmental impact.