Why idols of LORD GANESHA is immersed in to water?

VINAYAKA CHAVITHI is celebrated in the time of Badhra Padha Shukla and we place LORD GANESHA on that day with lot of devotion and we worship with 21 different prasadas after nine days (navarathri) we immerse LORD GANESHA in lakes, rivers etc. 

Why idols of LORD GANESHA immersed in to water? Here are the Reasons 

 LORD GANAPATHI Comes to the Earth to listen all the Devotes needs and he was to heaven water is the nearest way so all the idol of LORD GANESHA immerses into water.

And In olden days LORD GANESHA idol was made-up of Clay they thought that idols of LORD GANESHA made-up of clay so they decided to give to the back to the also the reason to immerse LORD GANESHA idols in to water 

And there are also some scientifically Importance behind immersing idols of LORD GANESHA in to water 

 During pooja of LORD GANESH we use many herbals etc they contain good medical values.  All that medical values gives the good results in the river which was polluted by the mixture of urine, skin diseases etc the leafs will release alkaloids in to water by that the  bacteria present in water will washed off and oxygen levels will be increased and these clay also helps to control floods and they also help to degrade the floods to back in to sand present in water maintains the level of water on the basis of these reasons also idol of  LORD GANESHA immersed in water.

Now days LORD GANESHA idol are being made-up of POP (PLASTER OF PARIS) using large amount of chemicals. When LORD GANESHA sculptures made-up of pop (pop plaster of Paris) when these LORD GANESHA POP Sculptures  are immersed in water bacteria level will increase a lot fishes, tortoise etc which living in water  (Aquatic animals) may  die and  skin diseases will increase a lot.