Picnic on Noordhoek beach and mouth to Wilde Voel Vlei

Questioning regarding Wilde Voel Vlei started after an outing with Imhoff Waldorf School which is situated 800 m in land from the beach. We celebrated Rudolf Steiners birthday, outside in what we all believed to be a clean environment .
Children and adults were unaware of the toxicity of the dead mussels that they were collecting on the rocks. I got suspicious after so many dead crabs were collected by the kids. It was an unconscious game of collecting the most dead crabs.
A couple of months later - I accompanied the Imhoff Waldorf Environmental classes to a clean up all the way to the beach and this time there were even more dead crabs a crab grave yard - the kids called it and the water was much greener and thicker in the river.