quote from insights:
Similarly, the Gemara later (25a) states that if excrement is being transported nearby, one may recite the Shema, because it is not considered in one's "area" ("Machaneh").
I think the gemorah says a moving excrement is forbidden . When a person is moving in an area full of excrement he may read k.s - please note the difference
Allan Katz , petach Tikve Israel
Excrement being transported is subject to an argument between Abaye and Rava. The reason stated in the Insights is true according to Abaye. Apparently, when a person is moving in an area full of excrement he cannot read Shema, according to both Abaye and Rava. Abaye would say that the Kavu'a area has excrement and it is therefore unfit to read Shema there (just as a Tamei standing under a tree causes a Tahor passing through to become Tamei), and Rava would say that the area is not Kadosh.
All the best,
Yaakov Montrose