Hamilton public health is warning residents to avoid all contact with water near Pier 4 in the city's harbour after discovering a toxic blue-green algae. In a media release Wednesday, officials suggested the following tips to avoid potential health risks: Avoid all contact with the water at the beach. If you do come into contact with water, rinse off as soon as possible with clean water. Both people and pets should not swim or wade in the water anywhere the algae is visible. The algae, also known as cyanobacteria, forms in shallow, warm, slow-moving water, according to public health.