The San Juan Islands, located 140 km north of Seattle in the heart of Salish Sea, is the most famous place for orca whale watching. Orca whales usually pass through the islands in greatest numbers between mid-May and mid-October when the salmon runs are strongest, although it's possible to spot them through the rest of the year. In March, April and late October you can see 50% fewer whales than in the summer. However, keep in mind that every year is different depending on the ecosystem.
While on the tour you can also expect to see Humpback Whales and Minke Whales, as well as sea lions and seals. Gray Whales can be spotted near Whidbey Island. There is also the scenic Deception Pass, which is worth exploring. Bald Eagles, porpoises, and other interesting seabirds inhabit the islands and are easily spotted near the shore.