diff --git a/src/raster/r.hydro.flatten/r.hydro.flatten.html b/src/raster/r.hydro.flatten/r.hydro.flatten.html
index e737be2704..b9e7568500 100644
--- a/src/raster/r.hydro.flatten/r.hydro.flatten.html
+++ b/src/raster/r.hydro.flatten/r.hydro.flatten.html
@@ -68,7 +68,8 @@ <h2>EXAMPLE</h2>
 
 <h2>REFERENCE</h2>
 Method based on workflow <a href="https://www.youtube.com/watch?v=p9KCfufNYgE">presented</a>
-at NC GIS Conference 2021 by Doug Newcomb.
+at NC GIS Conference 2021 by Doug Newcomb. Default value for percentile based on data from 
+<a href="https://ecos.fws.gov/ServCat/Reference/Profile/161439">presentation</a> made at FOSS4GNA 2023 
 
 <h2>SEE ALSO</h2>
 <em>