The Marines have a special kind of Scuba system (called a re-breather) that recycles the air for them, which prevents the bubbles from being seen from enemy sights. In recreational diving however, we only have a semi-closed re-breather, which partially recycles the air. It does not completely eliminate the bubbles, but it reduces them.
In one word... weights. Although it is all really about buoyancy.
Basically, people wear weights to make them sink. Then by adding small amounts of air to your BCD (Buoyancy Control Device) and controlling your breathing, you can 'cancel out' the effect of the weights when you get to the bottom to make you neutrally buoyant (effectively like being weightless).
A little more in depth;
Buoyancy is determined by an object's volume and weight. If the weight is more that the weight of the volume of water that it displaces the object is negatively buoyant (for example the weights that a diver uses). a SCUBA Diver uses this to get to the bottom, then when there adds air to the BCD. The air weighs less than the volume of water it displaces and is therefore positively buoyant.
Balancing the negative buoyancy of the weights with the positive buoyancy of the air should make you neutrally buoyant as the weight of the volume of water displaced is equal to the weight of the diver + equipment.
In the Water....
swallow water
Have a decent amount of weights, or dump the air from the vest. Vice versa for staying on the surface.
water proof ones
Lightning can be harmful to scuba divers because it can strike the water's surface and potentially electrocute anyone in the vicinity. Thunder, on the other hand, is not harmful to scuba divers but can indicate the presence of a thunderstorm, which can lead to dangerous conditions such as strong currents and rough seas. It is generally advised for divers to avoid entering the water during a thunderstorm or if lightning is present.
People are dumping trash in water.
They do not dive deep enough.
A float with a red flag with a diagonal white stripe is the symbol for "Divers Down"; SCUBA divers are underwater in this area. Be cautious in the area of the float, because the divers will surface nearby.
Generally no. They need to be quite fit to be able to swim in the water :)
Open Water
well there are myths saying that it did sink but submarines and scuba divers have checked the area which it was meant to sink but found nothing.....so i think its still floating in the water go n catch it ;)
Most scuba divers just obtain open water certifications from recreational diver training agencies, such as PADI, NAUI, BSAC or SDI.Only military or commercial divers undertake vocational diving qualifications.