How Many Rivers in the Western Hemisphere? Uncountable.

There is no answer. No global registry exists. The Western Hemisphere (longitudes 20°W–160°E) contains millions of streams—from the Amazon (6,400 km) to ephemeral desert washes that flow once a decade.

Why It’s Unanswerable

• Definition threshold: Perennial? Intermittent? Ephemeral? 1st order (no tributaries) vs. 12th order (Amazon)?
• Scale dependence: 1:24,000 map shows 100× more streams than 1:1,000,000.
• Dynamic: Channels shift, appear, vanish (avulsion, climate, human).
• Political: Data quality varies wildly (Canada/US: excellent; Amazon basin: sparse; Andes: steep, unmapped).

Best Estimates

• HydroSHEDS / HydroRIVERS (Lehner et al.): ~3.5 million river reaches globally (15 arc-sec). Western Hemisphere ≈ 1.5–2M.
• USGS NHDPlus: 2.7M flowlines (US only).
• Global river width database (GRWL): 500,000+ km of rivers >30 m wide.

Practical answer: "Hundreds of thousands of named rivers; millions of stream segments; infinite if you count every rill." Hydrologists work with network topology, not counts.