fill in(english)

we can no swim in the rivers, lakes and seas are dying as they have poisonous chemical.

we CANNOT swim in the rivers, lakes and seas (__BECAUSE__/__SINCE__/__AS__/_IF_ /__SUPPOSING THAT__/__IN CASE OF__/__IN THE EVENT OF__/__ON THE UNDERSTANDING THAT__) they have poisonous chemical.

We CANNOT swim in the rivers, lakes and seas if they have poisonous
chemical.

We CANNOT swim in the rivers, lakes and seas IF/ BECAUSE/AS they have poisonous chemical.

We CANNOT swim in the rivers, lakes and seas because they have poisonous chemical.