Mag. 400x
As seen here: http://protist.i.hosei.ac.jp/PDB/Images/Heterokontophyta/Araphidineae/Tabellaria/fenestrata.html and http://nordicmicroalgae.org/taxon/tabellaria%20fenestrata.
The 2nd image marks an attempt at communication. I'm sure of it!

• A pond-side water sample was taken on 12/27/2021 using a 10µ dip net. About 1/4" of ice had to be broken and pushed aside to access the water. Air temp. 36°F.