Found at almost all temperate seashores, rabid sea otter foam has been said to resemble soap suds. Rabid sea otter foam ranges from white to light mustard. The color of the foam depends on the rabidity of the sea otter, the darker the foam, the more rabid the sea otter. This phenomenon occurs when rabid sea otters foam at the mouth (a common symptom of hydrophobia). Soon after the foam leaves the sea otter's mouth, it drifts on top of the open sea where it later washes up on sand and gets stuck in between rocks. If any mammal comes into contact with the rabid sea otter foam, its chance of contracting the disease is nearly 60%. Due to the increasing amounts of rabid sea otter foam found on coastal shores, it is believed that almost a third of all sea otters are rabid. This could also be a probable factor in why the sea otter is endangered. 
Rabid Sea Otter Foam

Rabid sea otter foam washed up on temperate zone beach