Based on size:
* River: A larger body of flowing water.
* Ocean: A vast body of saltwater.
* Sea: Similar to an ocean, but usually smaller.
* Lake: A body of standing water.
Based on flow:
* Still water: A body of water that is not flowing.
* Stagnant: Not moving or flowing.
Based on location:
* Mountain: A high elevation landform.
* Desert: An arid, dry area.
* City: A densely populated urban area.
Other:
* Canyon: A deep, narrow valley, often with a river running through it.
* Gorge: Similar to a canyon, but usually smaller.
The best antonym for "creek" will depend on the specific context in which you are using the word.