Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ Quarterly Report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the quarterly period ended March 31, 2023 or ☐ Transition Report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Commission File Number 0-53713 OTTER TAIL CORPORATION (Exact name of registrant as specified in its charter) Minnesota 27-0383995 (State or other jurisdiction of incorpora ...