| Oyo River | |
| Name Other: | Sungai Oyo, Kali Oyo, Kali Ojo, Sungai Oya, Kali Oja |
| Pushpin Map: | Indonesia Java#Indonesia |
| Pushpin Map Size: | 285 |
| Pushpin Map Caption: | Location of river mouth |
| Source1 Location: | Wonogiri Regency |
| Mouth Location: | Bantul Regency |
| Mouth Coordinates: | -7.9558°N 110.3658°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Indonesia |
| Subdivision Type2: | State |
| Subdivision Name2: | Yogyakarta |
| Subdivision Type3: | Region |
The Oyo River is a river in southern Central Java and Yogyakarta, in the central south area of Java island, Indonesia.[1] It is a tributary of the Opak River.
It was the river on which the historical palaces of Mataram were located - Sultan Agung's Karta palace, and his son's Plered palace.
The river flows in the southwest area of Java with predominantly tropical monsoon climate (designated as Am in the Köppen-Geiger climate classification).[2] The annual average temperature in the area is 23 °C. The warmest month is October, when the average temperature is around 24 °C, and the coldest is January, at 22 °C.[3] The average annual rainfall is 2970 mm. The wettest month is January, with an average of 537 mm rainfall, and the driest is September, with 22 mm rainfall.[4]