Note 11 - Business Segment Information - Segment Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Revenue	$ 1,861,000	$ 1,364,000
Operating loss	(6,696,000)	(6,412,000)
Operating loss	6,696,000	6,412,000
Interest expense	(3,996,000)	(3,494,000)
Research and development	(1,472,000)	(1,719,000)
Tangible assets	1,728,000	1,292,000
Intangible assets	1,893,000	1,893,000
Corporate, Non-Segment [Member]
Operating loss	(4,248,000)	(4,185,000)
Operating loss	4,248,000	4,185,000
Interest expense	(3,944,000)	(3,494,000)
Research and development	(892,000)	(1,054,000)
Tangible assets	1,050,000	353,000
Intangible assets	1,893,000	1,893,000
Consolidation, Eliminations [Member]
Tangible assets	(59,000)	(6,000)
Intangible assets
Intersegment Eliminations [Member]
Research and development	603,000	600,000
Odor-No-More [Member] | Operating Segments [Member]
Revenue	1,459,000	1,123,000
Operating loss	(335,000)	(433,000)
Operating loss	335,000	433,000
Interest expense	(2,000)
Tangible assets	420,000	219,000
Intangible assets
Clyra [Member] | Operating Segments [Member]
Tangible assets	3,000	462,000
Intangible assets
BLEST [Member] | Operating Segments [Member]
Tangible assets	264,000	230,000
Intangible assets
BioLargo Water [Member] | Operating Segments [Member]
Operating loss	(728,000)	(801,000)
Operating loss	728,000	801,000
Research and development	(610,000)	(693,000)
Tangible assets	50,000	34,000
Intangible assets
BioLargo Engineering, Science & Technologies, LLC [Member] | Operating Segments [Member]
Revenue	999,000	863,000
Operating loss	(152,000)	(125,000)
Operating loss	152,000	125,000
Research and development	(354,000)	(374,000)
BioLargo Engineering, Science & Technologies, LLC [Member] | Intersegment Eliminations [Member]
Revenue	(597,000)	(622,000)
Clyra Segment [Member] | Operating Segments [Member]
Operating loss	1,233,000	868,000
Operating loss	(1,233,000)	(868,000)
Interest expense	(50,000)
Research and development	$ (219,000)	$ (198,000)