Note 9 - BioLargo Engineering, Science and Technologies, LLC (Details Textual) - USD ($)		1 Months Ended		3 Months Ended		12 Months Ended		25 Months Ended
	Nov. 04, 2019	Jan. 30, 2021	Sep. 30, 2017	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2019
Share-based Payment Arrangement, Noncash Expense, Total				$ 256,000	$ 801,000
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%	82.25%