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Note 2 - Summary of Significant Accounting Policies (Details Textual)			3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 05, 2025 USD ($)	Mar. 20, 2020 USD ($)	Jun. 30, 2025 USD ($)	Mar. 31, 2024 USD ($)	Jun. 30, 2025 USD ($) shares	Jun. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)	Oct. 22, 2021 USD ($)
Accounts Receivable, Allowance for Credit Loss, Current	$ 0		$ 134,000		$ 134,000		$ 97,000
Inventory Valuation Reserves			0		0		0
Asset Conversion, Accounts Receivable to Notes Receivable	$ 3,764,000				3,764,000	$ 0
Asset Conversion, Interest Rate	10.00%
Financing Receivable, after Allowance for Credit Loss	$ 3,572,000
Number of Patents Acquired								3
Income (Loss) from Equity Method Investments			7,000	$ (1,000)	9,000	$ (1,000)
Customer Deposit Liability, Current			158,000		158,000		90,000
Unrecognized Tax Benefits			$ 0		$ 0
Operating Lease, Weighted Average Discount Rate, Percent			18.00%		18.00%
Operating Lease, Right-of-Use Asset			$ 937,000		$ 937,000		992,000
Operating Lease, Liability			977,000		977,000		1,027,000
Finance Lease, Right-of-Use Asset, after Accumulated Amortization			$ 418,000		$ 418,000		451,000
Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)			3 years		3 years
Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)			10 years		10 years
Canadian Government Grants [Member] \| Minimum [Member]
Grant Term (Month)					6 months
Canadian Government Grants [Member] \| Maximum [Member]
Grant Term (Month)					18 months
ONM [Member]
Customer Deposit Liability, Current			$ 77,000		$ 77,000		14,000
CANADA
Customer Deposit Liability, Current			81,000		$ 81,000		76,000
Share-Based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares) \| shares					60,653,962
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares) \| shares					29,727,446
Odin Co Ltd [Member]
Payments to Acquire Interest in Joint Venture		$ 100,000
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage		40.00%
Odin Co Ltd [Member] \| Tomorrow Water [Member]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage		30.00%
Odin Co Ltd [Member] \| BKT and Tomorrow Water [Member]
Payments to Acquire Interest in Joint Venture		$ 150,000
Clyra Medical Technologies [Member]
Finance Lease, Right-of-Use Asset, after Accumulated Amortization			418,000		$ 418,000		451,000
Finance Lease, Liability			$ 405,000		$ 405,000		$ 448,000
Subsidiary, Ownership Percentage, Noncontrolling Owner			50.00%		50.00%		48.00%
BioLargo Engineering, Science & Technologies, LLC [Member]
Subsidiary, Ownership Percentage, Noncontrolling Owner			26.00%		26.00%		26.00%
BioLargo Energy Technologies, Inc (BETI) [Member]
Subsidiary, Ownership Percentage, Noncontrolling Owner			4.00%		4.00%		4.00%
Patents [Member]
Intangible Assets, Net (Excluding Goodwill), Total								$ 34,000
Customer Concentration Risk [Member] \| Accounts Receivable [Member]
Number of Major Customers					1
Customer Concentration Risk [Member] \| Revenue from Contract with Customer Benchmark [Member]
Number of Major Customers							1