Under Section 2 of the Water (Prevention and Control of Pollution) Act, 1974, Stream

• A river
• A watercourse (whether flowing or for the time being dry)
• Inland water (whether natural or artificial)
• Sub-terranean waters
• Sea or tidal waters to such extent or, as the case may be, to such point as the State Government may, by notification in the Official Gazette, specify in this behalf

The definition is deliberately wide to ensure comprehensive protection of all water bodies from pollution. No person is permitted to discharge any pollutant into a stream except under a consent granted by the State Pollution Control Board (Section 24).