Rank Name Source Destination Length 1 Mahaweli River Central
Province Trincomalee 335 km (208 mi) 2 Malvathu River Anuradhapura
Mannar 164 km (102 mi) 3 Kala Oya 148 km (92 mi) 4 Kelani River Sri
Pada Colombo 145 km (90 mi) 5 Yan Oya 142 km (88 mi) 6 Deduru Oya
142 km (88 mi) 7 Walawe Ganga 138 km (86 mi) 8 Maduru Oya 135 km
(84 mi) 9 Maha Oya 134 km (83 mi) 10 Kalu Ganga 129 km (80 mi) 11
Kirindi Oya 117 km (73 mi) 12 Kumbukkan Oya 116 km (72 mi) 13 Menik
Oya 114 km (71 mi) 14 Gin River Deniyaya Galle 113 km (70 mi) 15 Mi
Oya 109 km (68 mi) 16 Gal Oya 108 km (67 mi)
Related Q&A：
How many rivers are there in Sri Lanka？-Oh boy, that's a tricky question. Sri Lanka has a number of rivers, but it's not an easy number to pin down exactly. There are quite a few significant ones like the Mahaweli River, Kelani River, and Maha Oya. But when it comes to giving an exact count, it's a bit challenging. You see, some smaller rivers and tributaries might not be as well documented or widely known. I'd say there are probably several dozen rivers in total, but it could vary depending on how you define a \river\ and the level of detailed study. It's a beautiful country with a diverse waterway system though!
