Note 11 - BioLargo Engineering, Science and Technologies, LLC (Details Textual) - USD ($)		1 Months Ended		12 Months Ended		25 Months Ended
	Nov. 04, 2019	Jan. 30, 2021	Sep. 30, 2017	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2019
Share-based Payment Arrangement, Noncash Expense, Total				$ 2,071,000	$ 1,872,000
Percentage of Profits Interests Vested	2.50%	3.75%
Percentage of Option to Purchase Shares of Common Stock	10.00%	15.00%
Seven Employees Working at BioLargo Engineering, Science & Technologies, LLC [Member]
Deferred Compensation Arrangement with Individual, Requisite Service Period (Year)			5 years
Potential Ownership Percentage of Subsidiary Held by Subsidiary Employees Based on Performance			30.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross (in shares)	175,000	262,500		1,242,500	525,000
Incentive Issuance Stipulations for Subsidiary Employees, Accounts Receivable Collected by Year One of Operation			90.00%
Incentive Issuance Stipulations for Subsidiary Employees, Profit Earned in Year One of Operation			10.00%
Percentage of Profits Interests Vested				17.75%	11.25%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value	$ 44,000	$ 65,000		$ 135,000	$ 65,000
Seven Employees Working at BioLargo Engineering, Science & Technologies, LLC [Member] | Non-Qualified Stock Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross (in shares)			1,750,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)			5 years
Share-based Payment Arrangement, Noncash Expense, Total						$ 0
BioLargo Engineering, Science & Technologies, LLC [Member]
Noncontrolling Interest, Ownership Percentage by Parent			100.00%	82.00%