Thousand Islands

The Thousand Islands is the 80-km archipelago of 1,864 forested granite islands strung along the St. Lawrence River between Lake Ontario and the river's exit toward the Atlantic, straddling the Canada–US border between Ontario and New York State. The region's defining icons are Boldt Castle (the unfinished Gilded Age mansion on Heart Island, US side, abandoned 1904 when the owner's wife died and never restored) and the smaller Singer Castle on Dark Island (Canadian side, still privately operated). Boat tours run from Gananoque and Kingston on the Canadian side, Alexandria Bay on the US side; the Thousand Islands Bridge crosses the river at the eastern end. Season runs roughly mid-May through mid-October — the river ices over in deep winter. Climate is a humid-continental shoulder zone: warm muggy summers (highs 25-28°C in July, brief afternoon thunderstorms), brilliant autumn colors mid-September through mid-October, hard winters when the boats stop.

Plan your trip from

Climate, scoring, and month-by-month planning live on the page for the city you'd actually stay in:

When to go

Thousand Islands shares Ottawa's climate, so these are Ottawa's measured numbers — see the full month-by-month breakdown.

BEST TIME TO VISIT

Ottawa, Canada

INTEREST · Google Trends
☀ UV INDEX · typical midday peak
⚠ sunniest 1 in 10 days · UV reaches this or higher
🌫 PM2.5 air quality · on a typical day ⚠ worst 1 in 10 days · PM2.5 reaches this or higher

Best months: September, May, June

Tours & map

Tours and the map below are for Ottawa — the planning hub for Thousand Islands isOttawa, and Viator's catalog is keyed to cities rather than sub-locales, regions, or single attractions.

Tours in Ottawa

26 top-rated tours via Viator. Booking links earn this site a commission at no cost to you.

  1. 1Lilo Floating Tiki Bar on the Ottawa River (Gatineau Pickup)4.81★ (80)1h 30mfrom $61🔥 Selling fast
  2. 2Secrets of the Château Laurier Hotel Tour4.55★ (82)1h 15mfrom $27🔥 Selling fast
  3. 3Low Intensity Rafting on the Ottawa River | Day Trip4.90★ (58)8hfrom $159🔥 Selling fast
  4. 4Ottawa Food Tour with ByWard Market Flavors & 6 Local Tastings4.90★ (49)3hfrom $97🔥 Selling fast
  5. 5Canadian War Museum Admission4.63★ (243)3hfrom $19
  6. 6Cycling Ottawa's 200th Anniversary, self-guided4.85★ (48)4h 30mfrom $25
  7. 7Original Haunted Walk of Ottawa4.55★ (316)1h 15mfrom $27
  8. 8Ottawa City Highlights 3 Hour Walking Tour | Gratuity-Based4.68★ (215)3hfrom $5
  9. 9Ottawa Street Art Exploration Game and Self-Guided Tour3.95★ (21)from $7
  10. 10Ottawa Hop-On Hop-Off Sightseeing Tour4.28★ (512)1h 30mfrom $39
  11. 11Ottawa's Original Historical Highlights Public Walking Tour4.95★ (59)2hfrom $19
  12. 12Self-Guided Biking in Ottawa-Gatineau4.95★ (117)from $29
  13. 13Ottawa Premium City Tour with Parliament Hill & Canal Cruise4.37★ (195)4hfrom $101
  14. 14Ottawa 200th Anniversary Landmarks4.74★ (47)2hfrom $50
  15. 15Ottawa - Byward Market Food Tour5.00★ (26)3h 30mfrom $94
  16. 162-Hour Ottawa Express City Bike Tour4.97★ (317)2hfrom $57
  17. 17Flying Dress Photoshoot Experience in Ottawa5.00★ (17)1hfrom $398
  18. 18Hidden Ottawa Secrets Walking Tour4.67★ (9)1h 30mfrom $27🔥 Selling fast
  19. 19Ottawa Ecological Reserve Kayak Tour with TURTLE Sightings5.00★ (26)1h 45mfrom $54
  20. 20Ottawa Mystery Quest: Self-Guided Detective Adventure4.17★ (12)from $6
  21. 21National Gallery of Canada Admission4.69★ (26)from $18
  22. 22Ottawa Boat Cruise - Rideau Canal Cruise4.32★ (1,285)1h 30mfrom $43
  23. 23Ottawa Boat Cruise Paul's Boat Line4.34★ (1,004)1h 30mfrom $41
  24. 24Oh Canada Eh!? Ottawa Dinner Musical with Live Music and Comedy4.72★ (153)2hfrom $76
  25. 25Ottawa Embassy Quest: The Night You Don't Remember4.00★ (9)from $7
  26. 26Gatineau Park Nocturnal Snowshoeing Adventure & Dinner - From Ottawa & Gatineau4.95★ (39)3h 30mfrom $65

Last refreshed 2026-10-18.

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Common questions

When is the best time to visit the Thousand Islands?
Late June through August for warm-water boat tours and Boldt Castle access. Mid-September through early October for the autumn color (peak around Sept 25–Oct 5) and the lowest summer-mosquito risk. Boat operators run May to mid-October; Boldt Castle is open mid-May to mid-October only — book ahead in July–August.
Which Thousand Islands base — Gananoque, Kingston (Ontario), or Alexandria Bay (US)?
Gananoque is the most concentrated tourist base — boat tours every 90 min from the town dock, walking-distance to restaurants. Kingston (Ontario) is bigger and has its own attractions (Fort Henry, the Tragically Hip's hometown) — 30 min west. Alexandria Bay (NY, US side) is the alternative for visitors approaching from Syracuse / NYC. All three reach Boldt Castle in roughly equal travel time.
How long do I need for the Thousand Islands?
A day trip is the standard from Ottawa (1.5h drive), Kingston, or Toronto (3h). Overnight in Gananoque or Alexandria Bay lets you do both a daytime cruise AND a sunset cruise, plus Boldt Castle if you go in the morning. Two nights gives time for the 1000 Islands Parkway scenic drive.
Are the Thousand Islands really 1000 islands?
1,864 islands officially — definition is "land above water year-round, at least one square foot of surface area, supporting at least two trees." Many are barely larger than a kayak; the largest (Wolfe Island) has 1,400 residents. Use the Ottawa page for climate-month scoring covering the typical visit-base region.