The problem with reciting the Sh'ma whilst standing in a river is - that there is nothing covering one's body between his heart and his Ervah, 'Libo Ro'eh es ha'Ervah' is forbidden.
why is there no problem with the next gemara:
One is permitted to recite the Sh'ma - if Tzo'ah is visible through glass, but not if Ervah is visible through glass.
whats the difference between water and glass
Tanchem Frank, Jerusalem il
The distinction is not between water and glass, but rather between Tzo'ah and Ervah.
One may not recite Keri'as Shema in the presence of exposed Tzo'ah, as the verse says, "v'Chisisa Es Tzei'asecha" (Rashi). Glass is an acceptable way to cover Tzo'ah.
On the other hand, one may not recite Keri'as Shema when he sees Ervah because the Torah says, "v'Lo Yir'eh Becha Ervas Davar." Neither water or glass is an effective barrier to seeing Ervah.
Avraham Phillips