| Segment Reporting [Table Text Block] |
| | | Three Months Ended March 31, | |
| | | 2026 | | | 2025 | |
| Revenue | | | | | | | | |
| ONM Environmental | | $ | 423 | | | $ | 2,803 | |
| BLEST | | | 797 | | | | 690 | |
| Clyra Medical | | | 154 | | | | — | |
| BioLargo Canada | | | 58 | | | | 8 | |
| Intersegment revenue | | | (317 | ) | | | (232 | ) |
| Total | | $ | 1,115 | | | $ | 3,269 | |
| | | | | | | | | |
| Stock option expense | | | | | | | | |
| BioLargo corporate | | $ | 286 | | | $ | 409 | |
| Clyra Medical | | | 413 | | | | 206 | |
| Total | | $ | 699 | | | $ | 615 | |
| | | | | | | | | |
| Depreciation expense | | | | | | | | |
| BioLargo corporate | | $ | (9 | ) | | $ | (11 | ) |
| ONM Environmental | | | (10 | ) | | | (10 | ) |
| BLEST | | | (11 | ) | | | (17 | ) |
| Clyra Medical | | | (2 | ) | | | (4 | ) |
| BETI | | | (2 | ) | | | — | |
| Total | | $ | (34 | ) | | $ | (42 | ) |
| | | | | | | | | |
| Research and development expense | | | | | | | | |
| BioLargo corporate | | $ | (261 | ) | | $ | (248 | ) |
| BLEST | | | (208 | ) | | | (244 | ) |
| BETI | | | (142 | ) | | | (60 | ) |
| BioLargo Canada | | | (92 | ) | | | (136 | ) |
| Clyra Medical | | | (521 | ) | | | (335 | ) |
| Intersegment R&D | | | 317 | | | | 232 | |
| Total | | $ | (907 | ) | | $ | (791 | ) |
| | | | | | | | | |
| Operating income (loss) | | | | | | | | |
| BioLargo corporate | | $ | (459 | ) | | $ | (817 | ) |
| ONM Environmental | | | (95 | ) | | | 956 | |
| BLEST | | | (380 | ) | | | (378 | ) |
| BETI | | | (355 | ) | | | (94 | ) |
| BEST | | | (90 | ) | | | (58 | ) |
| BioLargo Canada | | | (113 | ) | | | (156 | ) |
| Clyra Medical | | | (1,712 | ) | | | (1,315 | ) |
| Total | | $ | (3,204 | ) | | $ | (1,862 | ) |
| | | | | | | | | |
| Interest income (expense) | | | | | | | | |
| BioLargo corporate | | $ | 63 | | | $ | 3 | |
| ONM Environmental | | | — | | | | 15 | |
| Clyra Medical | | | (179 | ) | | | (83 | ) |
| Total | | $ | (116 | ) | | $ | (65 | ) |
| | | | | | | | | |
| Net income (loss) | | | | | | | | |
| BioLargo corporate | | $ | (481 | ) | | $ | (815 | ) |
| ONM Environmental | | | (95 | ) | | | 971 | |
| BLEST | | | (380 | ) | | | (377 | ) |
| BETI | | | (355 | ) | | | (94 | ) |
| BEST | | | (90 | ) | | | (58 | ) |
| BioLargo Canada | | | (113 | ) | | | (150 | ) |
| Clyra Medical | | | (1,891 | ) | | | (1,398 | ) |
| Total | | $ | (3,405 | ) | | $ | (1,921 | ) |
| As of March 31, 2026 | | BioLargo | | | ONM | | | CLYRA | | | BLEST | | | BETI | | | BioLargo Canada | | | Elimination | | | Total | |
| Tangible assets | | $ | 674 | | | $ | 2,016 | | | $ | 3,520 | | | $ | 1,022 | | | $ | 235 | | | $ | 12 | | | $ | (203 | ) | | $ | 7,276 | |
| Operating lease right-of use | | | 206 | | | | — | | | | 169 | | | | 604 | | | | — | | | | — | | | | — | | | | 979 | |
| Finance lease right-of-use | | | — | | | | — | | | | 310 | | | | — | | | | — | | | | — | | | | — | | | | 310 | |
| Total | | $ | 880 | | | $ | 2,016 | | | $ | 3,999 | | | $ | 1,626 | | | $ | 235 | | | $ | 12 | | | $ | (203 | ) | | $ | 8,565 | |
| As of December 31, 2025 | | BioLargo | | | ONM | | | CLYRA | | | BLEST | | | BETI | | | BioLargo Canada | | | Elimination | | | Total | |
| Tangible assets | | $ | 694 | | | $ | 2,331 | | | $ | 2,650 | | | $ | 1,169 | | | $ | 4 | | | $ | 321 | | | $ | (224 | ) | | $ | 6,945 | |
| Operating lease right-of use | | | 238 | | | | — | | | | 175 | | | | 615 | | | | — | | | | — | | | | — | | | | 1,028 | |
| Finance lease right-of-use | | | — | | | | — | | | | 338 | | | | — | | | | — | | | | — | | | | — | | | | 338 | |
| Total | | $ | 932 | | | $ | 2,331 | | | $ | 3,163 | | | $ | 1,784 | | | $ | 4 | | | $ | 321 | | | $ | (224 | ) | | $ | 8,311 | |
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