Authorities on Friday gave the all-clear to the water near Dubai Marina. They said the change in colour was caused by a chemical named Bentonite. Bentonite only changes the colour of water and there are no harmful effects on health and the environment. Qarn 
The substance flowed into the water from a construction site inAl Sabkha. Dubai Municipality said the site is connected to the Marina through a drainage system. The orange-red colour of the water was first noticed on Thursday and social media was soon abuzz with pictures.
On Friday morning, the bright colour turned muddy brown. The murky water spread over at least 1.5km, beyond Marina Mall, towards the south end, near Choithrams and closer to Jebel Ali. But there was no foul smelli n the area.
Eng. Talib Julfar, Assistant Director-General of Dubai Municipality for Environment and Public Health Services Sector, said a nearby construction site was probably the reason for the change in the colour of the water.

source: Khaleejtimes