Live On the Sea Floor

Our planet earth is not so small, We have enough space accommodate to all. Our lands already have been occupied by us, But our ocean floors have vast area which are marvellous. We know someday low lying countries will submerge, So why we don't build under sea colonies. Let's think about it seriously, We don't need to go to either the Mars or the moon shortly. We can build houses on the sea floor's layer, We know it's really hard to cope with water pressure. But it is not impossible for us at all, We can use our modern technology to make this possible. Might be today this idea is science fictional, I am quite sure tomorrow it will be real.