| Sulak | |
| Pushpin Map: | Caucasus mountains#Russia Dagestan |
| Mouth Coordinates: | 43.256°N 47.546°W |
| Subdivision Type1: | Country |
| Length: | 144km (89miles) |
| Discharge1 Avg: | 176m3/s |
| Basin Size: | 15200km2 |
| Tributaries Right: | Avar Koysu |
The Sulak (Russian: Сула́к, Kumyk: Сулак (Sulak)/Къой-сув (Qoysuw), Chechen: Ġoysu[1]) drains most of the mountainous interior of Dagestan northeast into the Caspian Sea. It and most of its branches flow in canyons. Its main tributaries are, from north to southeast:
North of the Sulak basin is the Terek basin and south of it is the Samur basin. To the west is the crest of the Main Caucasian Range of the Caucasus Mountains and to the east are many short rivers that flow down into the Caspian.
The Sulak proper starts at the junction of the Andi and Avar Koysus. It flows northeast into the broad Chirkey Reservoir. It then flows northwest through the narrow Miatli canyon and reservoir. It reaches flat country at Miatli and leaves the last mountains just south of Kizilyurt and enters the Terek-Sulak Lowland about 50km (30miles) from its source. Here there are meanders, former channels and canals. It flows northeast about 25km (16miles), turns east and reaches the Caspian after about 50km (30miles). Its delta is a smaller version of the Terek River delta about 66km (41miles) north. The lower Sulak supplies water to Makhachkala through a canal.In 1735 the Sulak River was stipulated as defining the boundary between the Russian and the Persian empires.