Exhibit 31.3

CERTIFICATION OF PRINCIPAL EXECUTIVE OFFICER

PURSUANT TO RULE 13a-14(a)
AS ADOPTED PURSUANT TO
SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

I, Dennis P. Calvert, certify that:

(1)         I have reviewed this Amendment No. 1 to Annual Report on Form 10-K of BioLargo, Inc.; and

(2)         Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report.

/s/ Dennis P. Calvert

Dennis P. Calvert

Chief Executive Officer
BioLargo Inc.
Date: April 30, 2026