Are there nonstop flights from Seattle (LKE) to Rosario (RSJ)?

Yes. Kenmore Air fly this route. Flight time is about 38m.

Seattle → Rosario

Kenmore Air Harbor Seaplane Base (LKE) to Rosario Seaplane Base (RSJ)・120 km

Nonstop flights available (1 airline). Flight time about 38m. Nonstop return flights also operate.

Times are estimated from distance. Check schedules, frequency and availability with the airline or a booking site.