Also known as: Kalu River, Black River
Headwaters from Adam's Peak/Sri Pada; upper river near Sinharaja rainforest; tea/rubber then coconut plantations; gem country (Ratnapura); mangrove estuary at Kalutara

Whether there is a river here on your dates, and what kind of water it is.
Rainfall/monsoon-fed tropical river from Sri Pada (Adam's Peak) and Sinharaja; dry-season discharge ~10-20 m3/s, SW-monsoon peaks can exceed ~2600 m3/s. Confirm.
Runnable much of the year at manageable levels; avoid monsoon flood spikes. Confirm.
Monsoon May-Sep swells the rivers (Ratnapura is the wettest region) for biggest water; dry season Dec-Apr calmer; runnable much of the year, avoid peak-flood spikes. Confirm.
Warm tropical throughout, no wetsuit needed; river bathing at camps
Ratnapura basin is notoriously flash-flood prone; steep forested upper catchment; gauges at Putupaula and Ellagawa; high-rain days dangerous and unrunnable
A river changes grade with its level. These grades describe a normal flow - in flood the same run is harder, and often a different run entirely. Check the gauge before you commit.
Class I-II (occasional II-III at the Ellagawa drop in higher flow); some blogs wrongly cite grade 4-5 - Confirm.
Canoeing; Kayaking
Built-in - 1-day (Ratnapura to Ellagawa, easiest), 2-day and 3-day to Kalutara (for experienced canoeists); calm upper vs livelier lower segment
Upper calm section beginner/family friendly; full multi-day / lower faster water for fitter experienced paddlers
Ellagawa rapid, a ~4 ft drop by the bridge, is the only real technical spot; wave trains and swirls below Ellagawa; otherwise slow water
Ellagawa rapid can be portaged/lined at the bridge; flood-driven high flow, strainers/debris after rain, populated urban start, tidal influence near Kalutara
Ratnapura (Saman Devalaya) to Ellagawa (1-day); continuing to Kiriella / Anguruwatota / Kalutara (multi-day)
Markedly quieter than Kitulgala - secluded, birds and the paddle the only sounds
No specific river permit/concession found; sold as packaged guided tours; indicative kayak day-trip pricing from ~USD 90. Confirm.
Permits and operators change - confirm before booking.
Put-in at Saman Devalaya easily road-accessible ~3 km from Ratnapura main bridge; take-outs at road-connected villages/bridges (Ellagawa, Kiriella, Anguruwatota, Kalutara)
Operator-run - gear/camp kit trucked to campsites ahead; guided transfers; Ratnapura ~2 hr from Colombo
Eco Team fully-serviced riverside campsites at Kiriella (and Wagawatta/Anguruwatota) - pre-set tents, kitchen, toilets, showers, meals
Provided - canoes/kayaks, PFDs, helmets, paddles; water shoes, dry bag advised; coverage decent in populated corridor, patchy in jungle (est)
Ratnapura; Colombo ~2 hr; Kalutara at river mouth; Kitulgala neighbouring hub
Flash flooding is the primary danger (Ratnapura basin); big seasonal flow swings; urban/polluted start; estuary tidal near Kalutara; grade claims vary - confirm difficulty with operator
Route runs through/near villages and road bridges for frequent road egress; guides carry safety gear
Guided expeditions standard - certified guides/instructors, life jackets and helmets provided, safety briefing
This profile is desk research, compiled from public sources - not a first-hand river run report. Coordinates are approximate.