Oyo River

Oyo River or Kali Oyo or Oya River or Kali Oya is one of the major rivers in Gunung Sewu Geopark in Yogyakarta Province, Indonesia, upstream on the western slopes of the Gajahmungkur and Kukusan Mountain Hills in Wonogiri District, Central Java Province.

The river flows along 106.75 kilometers from the northeast to the southwest until it empties into the Opak River in Bantul Regency. The monthly water debit is 9.31 cubic meters per second with a maximum of 83.2 cubic meters per second and a minimum of cubic meters per second.

The Oyo River is a periodic river that flows across the northern and southern karst hills with a flow of suspended load. The river has many tributaries including the Buyuk River, Jurang River, Lunyu River, Kedunggedang River, Ngalang River, Widoro River, Juwet River, Saradan River, Pentung River, Kaliurang River, and Prambutan River.

Geomorphology and Hydrology

The geomorphology of the river is formed by the arrival of water which is concentrated in the burdens of the burly karst rocks caused by erosion agents, tectonic factors that occur at the beginning of the stage, and significant temperature changes.

The Oyo River starts from upstream through the Wonogiri Regency area in Central Java Province, then passes Gunung Kidul Regency and Bantul Regency in Yogyakarta Province. The river is included in the Opak River basin with the Oyo watershed sub-area covering 639 square kilometers.

The river is in the southern region of the island of tropical tropical climate for the Am code according to the Köppen-Geiger climate classification. The average temperature of a year is around 23 Celsius. The hottest is October at an average temperature of 24 Celsius and the coldest is January at 22 Celsius. The average annual rainfall is 2970 mm. The month with the highest rainfall is January for an average of 537 mm and the lowest is September for an average of 22 mm.

Rafting and tubing

Oyo River is a place for outdoor activities and semi adventure along the river. The tourists do white water rafting using rubber boats during the rainy season, but river tubing is more often done when the water discharge is small. Oyo River Waterfall is the most interesting spot to take pictures during an adventure.

Fish

The Oyo River is home to Nilem or Melem (Osteochilus vittatus) which has a total length of up to 260 mm, a height at the beginning of the dorsal fin of up to 4 mm, and a head length of up to 4.5 mm. The snout is round and the wrinkled lips can be raised. This fish is a family with Goldfish, but the mouth is lower and the body is elongated like Braskap fish.

Other fish found in the Oyo River are Suckermouth catfish (Hypostomus plecostomus), Wader (Puntius javanicus), Tawes (Barbonymus gonionotus), Javanese catfish or Lele Jawa (Clarias batracus), Dumbo catfish or Lele dumbo (Clarias gariepinus), and Snakehead murrel (Channa striata).

Insect

Phlaeoba fumosa, Phlaeoba infumata, Trilophidia annulata, Oxya sinensis, Oxya japonica, Caryanda spuria, Atractomorpha crenulata, Acrida cinerea, Conocephalus sp, Caedicia simplex, Phaneroptera falcata, Locusta migratoria, Valanga nigricornis, Dissosteira carolina, Gryllus sp, Teleogryllus mitratus, Tetrix sp, Appias lyncida.

Appias olferna, Catopsilia pomona, Eurema blanda, Acraea violae, Danaus chrysippus, Hypolimnas bolina, Junonia almana, Junonia atlites, Junonia orithya, Mycalesis mineus, Phalanta phalanta, Yoma sabina, Chilades pandava, Zizina otis, Zizula hylax, Taractrocera archias, Orthetrum sabina, Pseudagrion rubriceps.

Ischnura senegalensis, Trithemis aurora, Pantala flavencens, Libellago lineata, Copera marginipes, Brachytemis contaminata, Crocothemis servilia, Rhynocypa fenestrata, Diplacodes trivialis, Prodasineura autumnalis, Neurothemis terminata, Ictinogomphus decoratus, Paragomphus reinwardtii, Potamarcha congener, Agriocnemis femina.