The following is a guide to Toiveling Keilim in natural bodies of water, which are Kosher for Toiveling Keilim:
Sea: Any ocean or sea, or an inlet, estuary, bay, etc. fed from the ocean or sea is Kosher for Toiveling Keilim. A beach off the ocean is Kosher for Toiveling Keilim.
River: Rivers are only Kosher for Toiveling Keilim if the following conditions are met: (a) They continue flowing even after the rainy season has ended and all snow on nearby mountains has finished melting, (b) Currently the majority of the water in the river is fed from underground water, and NOT from rainwater, (c) no turbines along the river. Being that this is hard to ascertain, a river should NOT be used to Toivel Keilim.
Spring: Any natural spring is Kosher for Toiveling Keilim.
Lakes: If they have no outlet, and no control valves, they are Kosher for Toiveling Keilim.
Remove all stickers that are present on the Keilim.
If the Keili has multiple parts which are connected to each other, and are made to be removed (for cleaning, etc.), the parts should be separated before Toiveling.
The Keilim should be fully immersed in the water, and covered by the water.
The Toiveling should be done by a Jew over Bar / Bas Mitzvah, or a Jewish child with his parent supervising him.
Any Keili which is used for preparation, cooking, serving or storage of food and is made from: metal, glass or solid material such as Corelle or Corningware - needs to be Toiveled.
When Toiveling a Keili made from metal, glass or solid material such as Corelle or Corningware - a Bracha should be recited (אשר קדשנו במצוותיו וצוונו על טבילת כלי / כלים).
Plastic Keilim made for regular use (not disposable) should be Toiveled without a Bracha.
A Keili which was made by a Jew, or a wholly Jewish-owned company need not be Toiveled, regardless of the material it is made from.
Disposable utensils or pans, which will not be reused, need not be Toiveled, regardless of the material they are made from. However, if one intends to reuse them - one should Toivel them without a Bracha before the first use.
A Keili which is reusable, needs to be Toiveled even if it will only be used once.
Regarding electric Keilim, the removable parts which are made from glass or metal, and touch the food directly - should be Toiveled.