Padilla Bay is a large, shallow saltwater estuary located in Skagit County, Washington, USA. It is approximately eight miles long and three miles wide, forming part of the intertidal Skagit River delta where it meets the Salish Sea. The bay is characterized by its extensive mudflats and eelgrass beds, which become fully exposed during low tide. The average high-tide depth is only 6 to 8 feet, and at low tide, the bay floor is easily walked. This extreme tidal range is the primary consideration for paddlers, who must plan trips carefully to avoid being stranded on expansive mudflats. Tides lower than 3 feet begin to uncover sand bars. The bay's shallow nature and large surface area mean it can develop significant fetch, making it susceptible to wind-driven waves, though conditions are sheltered overall.

Key public launch points for paddlers include Bay View State Park, which offers a boat launch and requires only a short walk from the parking lot to the beach, and March Point, a public boat ramp located at 10298 March's Point Road. The Swinomish Channel Boat Launch, with two ramps, provides another access point near the northern entrance to the channel. The Padilla Bay National Estuarine Research Reserve features an interpretive center with exhibits, and while it has trails and an observation deck, its shoreline access for launching watercraft is limited to a beach reachable via a spiral staircase from the deck.

The bay is part of a major migratory bird corridor along the Pacific Flyway, offering exceptional wildlife viewing. The extensive eelgrass habitat supports a rich ecosystem, attracting herons, ducks, black brants, eagles, otters, and seals. Winter brings large flocks of snow geese. Paddlers can explore the bay itself or use it as a gateway to nearby islands such as Saddlebag, Hat, Guemes, Vendovi, Samish, and Cypress Islands, some of which host Cascadia Marine Trail campsites. Routes to these islands can vary in difficulty from Sea Kayak II to III+. The Swinomish Channel, connecting to the bay, offers calm, scenic paddling but also becomes very shallow at low tide, requiring tide table consultation. Boat traffic, particularly in the channel and near marinas, is a hazard to watch for. Standard rules apply for protected areas and Marine Trail campsites.