The two gulls are both Ring-billed Gulls in the Niagara River just below the falls.
The foam at the lower right of the photo consists of clay, diatoms and other forms of algae. It is naturally occuring and is not toxic. The clay comes from the mist (water) as it evapoates while going over the falls. Eventually, as it moves downstream it remixes with the water and disappears. It also appears in the area of the Whirlpool, further downstream.
