Note 2 - Summary of Significant Accounting Policies (Details Textual)			3 Months Ended		9 Months Ended
	Jun. 06, 2025 USD ($)	Mar. 20, 2020 USD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) shares	Sep. 30, 2024 USD ($)	Aug. 05, 2025 USD ($)	Dec. 31, 2024 USD ($)	Oct. 22, 2021 USD ($)
Accounts Receivable, Allowance for Credit Loss, Current			$ 700,000		$ 700,000			$ 97,000
Provision for Loan, Lease, and Other Losses					3,849,000
Inventory Valuation Reserves			0		0			0
Number of Patents Acquired									3
Income (Loss) from Equity Method Investments			9,000	$ (3,000)	9,000	$ (4,000)
Customer Deposit Liability, Current			80,000		80,000			90,000
Unrecognized Tax Benefits			$ 0		$ 0			0
Operating Lease, Weighted Average Discount Rate, Percent			18.00%		18.00%
Operating Lease, Right-of-Use Asset			$ 1,070,000		$ 1,070,000			992,000
Operating Lease, Liability			1,111,000		1,111,000			1,027,000
Finance Lease, Right-of-Use Asset, after Accumulated Amortization			$ 400,000		$ 400,000			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			$ 1,000		$ 1,000			14,000
CANADA
Customer Deposit Liability, Current			79,000		$ 79,000			76,000
Share-Based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares) | shares					63,781,849
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares) | shares					28,980,918
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			400,000		$ 400,000			451,000
Finance Lease, Liability			$ 383,000		$ 383,000			$ 448,000
Subsidiary, Ownership Percentage, Noncontrolling Owner			52.00%		52.00%			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] | Revenue from Contract with Customer Benchmark [Member]
Number of Major Customers			1	1	1	1
Customer Concentration Risk [Member] | Accounts Receivable [Member]
Number of Major Customers					1	1
Royalty Receivable [Member]
Financing Receivable, before Allowance for Credit Loss							$ 463,520
Financial Asset, Past Due [Member] | Product Invoice Receivable [Member]
Financing Receivable, before Allowance for Credit Loss	$ 2,385,468
Receivable with Imputed Interest, Effective Yield (Interest Rate)	10.00%
Financial Asset, Past Due [Member] | Royalty Receivable [Member]
Financing Receivable, before Allowance for Credit Loss	$ 1,378,141
Receivable with Imputed Interest, Effective Yield (Interest Rate)	10.00%