| Poronay | |
| Name Other: | 幌内 |
| Name Etymology: | Ainu for "big river"[1] |
| Map: | Location of mouth of Poronai River.png |
| Subdivision Type1: | Country |
| Subdivision Name1: | Russia |
| Subdivision Type2: | State |
| Subdivision Name2: | Sakhalin Oblast |
| Length: | 350km (220miles) |
| Discharge1 Location: | Pacific Ocean[2] |
| Discharge1 Avg: | 120m3/s |
| Source1: | Mount Nevel |
| Source1 Location: | East Sakhalin Mountains |
| Source1 Coordinates: | 50.372°N 143.1823°W |
| Mouth: | Gulf of Patience |
| Mouth Location: | Sea of Okhotsk |
| Mouth Coordinates: | 49.2255°N 143.1232°W |
| Basin Size: | 7990km2 |
The Poronay (Russian: Поронай, Japanese: 幌内川) is the longest river on the island of Sakhalin in Russia. It flows in a southerly direction through Tym, Smirnykhovsky and Poronaysky Districts.
The river begins on Mt. Nevel in the East Sakhalin Mountains, flows south through the swampy wetlands of the Tym-Poronay Valley, and enters the Sea of Okhotsk in the Gulf of Patience. 10abbr=onNaNabbr=on before it enters the sea, the river divides into two arms, which flow into the sea 5abbr=onNaNabbr=on apart from each other. The two branches create a marshy river island in the middle. The town of Poronaysk is located near the western mouth of the river.
The Poronay is crossed by only two bridges, one rail and one road bridge. Both bridges are next to each other, in the middle of the river between the towns of Pobedino and Pervomaysk. The river valley, especially the area between the downstream Poronay and the Deer River (a small river to the east), has many lakes. The Poronay river system is a rich breeding ground for salmon[3] and other anadromous fish, as well as freshwater fish such as Amur pike.[4]
The river is fed by both snowmelt and rain. Average water flow is 120 m³/s. The highest level of flow has been observed in early May, and the lowest in the second half of September. The river usually freezes in the second half of November, while the ice thaws in late April.
The length of each tributary is given in parentheses: