1)
Did the land breed Tzfarde'im?
1.
Rashi (from Shocher Tov): Wherever water spread, Tzfarde'im spread.
2.
Radak: No, the river bred them - "v'Sharatz ha'Y'or Tzfarde'im" (Shemos 7:28). It says Artzam, for wherever there was water in their land, Tzfarde'im spread - "Al ha'Naharos Al ha'Y'orim v'Al ha'Agamim" (Shemos 8:1).
2)
Why does it say "Sharatz" (masculine singular)?
1.
Radak #1: The suffix "Eretz" is masculine, e.g. "v'Lo Nasa Osam ha'Aretz" (Bereishis 13:6).
2.
Radak #2: Refer to 105:30:1:2.
3.
Malbim (from Tanchuma Va'era 14): One Tzfarde'a rose, and it emitted many Tzfarde'im.
