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Note 1 - Business and Organization (Details Textual)	12 Months Ended
Note 1 - Business and Organization (Details Textual)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total	$ (11,440,000)	$ (10,696,000)
Net Cash Provided by (Used in) Operating Activities, Total	(4,422,000)	(3,891,000)
Working Capital	3,289,000
Assets, Current, Total	1,065,000	955,000
Revenue from Contract with Customer, Including Assessed Tax	1,861,000	1,364,000
Cash Provided by Financing Activities	4,466,000
Cash and Cash Equivalents, at Carrying Value, Ending Balance	$ 655,000	$ 655,000	$ 990,000
Number of Wholly-Owned Subsidiaries	4
BioLargo Engineering, Science & Technologies, LLC [Member]
Noncontrolling Interest, Ownership Percentage by Parent	97.50%			100.00%
Biolargo [Member] \| Clyra Medical Technology Inc [Member]
Noncontrolling Interest, Ownership Percentage by Parent	36.00%
Convertible Notes, Maturing August 12 and 16, 2020 [Member]
Convertible Notes Payable, Total	$ 550,000