I wanna make in my map the green smoke/fog for the hazard water.
What enties do I need etc.
Please help.

-Create an info_particle_system. Place it directly on the surface of your toxic pool.
-Set it's effect name property to one of the following, depending on the dimensions you want:
water_mist_1024_512
water_mist_256
water_mist_384_128
water_mist_512
water_mist_512_128
And there you go, perfect toxic fog effect.

Thank you dude