Salinisation occurs when water added to the soil during irrigation evaporates directly from the moist soil, causing salt to be left behind on the soil after evaporation.

Salinization can also occur following irrigation when there is no proper drainage of excess water. the groundwater may reach the upper soil layers, bringing up dissolved salts from the ground. Saline salts are those in which the concentration of salts is too high for crops to grow well. 

Chemicals (fertilizers / pesticides) reach the streams and rivers, they become nutrients for algae to grow on the surface of water. This causes eutrophication which is the presence of excess nutrients in water, leading to algae bloom. Algae bloom depletes oxygen in the water and block sunlight from reaching aquatic plants. This results in the death of aquatic plants and other organisms which then decomposes and further depletes oxygen.