Note 10 - BioLargo Energy Technologies, Inc. (Details Textual) - USD ($)	3 Months Ended
	Sep. 30, 2025	Mar. 31, 2024	Jan. 01, 2023
BETI Common Stock [Member]
Investment Owned, Balance, Shares (in shares)	25,000
Conversion of BETI Stock into BioLargo Stock [Member]
Conversion of Stock, Shares Converted (in shares)	25,000
Conversion of Stock, Shares Issued (in shares)	153,261
BioLargo Energy Technologies, Inc (BETI) [Member]
Stock Issued During Period, Shares, New Issues (in shares)	27,017	20,000
Shares Issued, Price Per Share (in dollars per share)	$ 3.7	$ 2.5
Proceeds from Issuance or Sale of Equity	$ 100,000	$ 50,000
Stock Conversion, Discount on Volume Weighted Average Price		20.00%
Shares, Outstanding (in shares)	9,514,027
BioLargo Energy Technologies, Inc (BETI) [Member]
Investment Owned, Balance, Shares (in shares)	9,095,000		9,000,000
Subsidiary, Parent Ownership Interest	96.00%