Yes, ArcSWAT is compatible with ArcGIS 10.8.1. The latest version, ArcSWAT 2012.10.26 (released on August 18, 2023), supports ArcGIS 10.8 and is available for download. Installation Recommendations:

• Uninstall Previous Versions: Before installing the new version of ArcSWAT, ensure that any previous versions are uninstalled to prevent potential conflicts.
• .NET Framework Requirement: Ensure that the .NET Framework 2.0 is installed on your system prior to installing ArcGIS. This is necessary for ArcGIS DOTNet support to function correctly.

​ArcSWAT, the ArcGIS extension for the Soil and Water Assessment Tool (SWAT), has specific compatibility considerations with various versions of ArcGIS. As of the latest available information, ArcSWAT is officially compatible up to ArcGIS 10.8. Compatibility with ArcGIS 10.8.1 is not explicitly stated, and users have reported issues when attempting to use ArcSWAT with this version.

Recommendations:

• Use ArcGIS 10.8: To ensure compatibility, it's advisable to use ArcSWAT with ArcGIS 10.8, for which it is officially supported.​
• Upgrade to ArcGIS 10.8.2: If you prefer a more recent version, consider upgrading to ArcGIS 10.8.2. ArcSWAT 2012.10_8.25 has been confirmed to be compatible with ArcGIS 10.8.2 (build 28388).
• chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://swat.tamu.edu/media/i40diuza/arcswat_version20121025_releasenotes.pdf
• Consider ArcGIS Pro: An ArcSWAT add-in for ArcGIS Pro (BETA version) was released in December 2024. If you have access to ArcGIS Pro, this could be a viable alternative. ​swat.tamu.edu

Installation Tips:

• Ensure .NET Framework is Installed: Before installing ArcSWAT, ensure that the .NET Framework 2.0 is present on your computer, as it's required for ArcGIS DOTNet support. ​swat.tamu.edu
• Follow Installation Guides: Detailed installation instructions and videos are available on the official ArcSWAT website to assist with the process. ​swat.tamu.edu

Thanks you for your response !

Download at: https://swat.tamu.edu/software/arcswat/

AcrcGIS Compatibility:

• ArcSWAT 2012.10_8.25 is compatible with ArcGIS 10.8.2, build 28388.

SWAT2012.exe Version:

• The SWAT2012.exe Revision 687 is packaged with ArcSWAT 2012.10_8.25.

Changes from Version 2012.10_7.24:

Note: This information has been taken from Jaclyn Tech (Google Groups)