Along the boardwalk trails at Boundary Bay Regional Park, they have signs that say:
"Baby birds on the ground!"
For the next few months, some birds will be nesting on the ground in the park. Please stay on trails and keep all dogs on a leash. - Greater Vancouver Regional District Parks Department
As the trails that lead through the local wetlands are on boardwalks, do respect local wildlife, and remain on those boardwalks - they're there for a reason!
In Boundary Bay Regional Park, they're quite specific that your dog stays on its leash along the trails. These trails are located along boardwalks and beside wetland ecosystems - popular with local wildlife and nesting birds. However, it appears that dogs may be unleashed with supervision at Centennial Beach, once you're out along the sand at low tide.
As well, the park provides little plastic bags so you can clean up after your dog. As you can see from the photo, they have really cute signs illustrating how to do it!