NOAA, the National Oceanic and Atmospheric Administration, has some great, free, educational games that teachers can use with their students.
There are over 25 different games and interactive activities that cover topics about water, air, the oceans, environmental issues and ocean life. Many of the games and activities are hosted on other sites, but gathered here for easy access
WaterLife: Where Rivers Meet the Sea is a game based on the ecosystem of a United States west coast estuary. It helps students learn about estuaries, food webs, and why estuaries are essential to ocean life and to humans.
This is a great way to have students learn about the oceans, air, and the environment while having fun playing a game.