Most speculation has the slaves toiling on the two dams which
contained water in Lake Moeris which was let out gradually to
keep the Nile flowing all year.

Where in most stories Moses parted the Red Sea for the slaves to
escape there is new evidence which suggests this might be a mis-
translation and it was actually "the Sea of Reeds" which was parted.
This would be consistent with low water levels in the Nile and an
escape ahead of a torrent of water let loose by a cut in an earthen
dam. The loss of this water supply might also have led to very hard
times in Egypt until a new crop came in the following year.

The "marsh of reeds" could have been the low lying areas west of the
pyramids. Papyrus was of great value to the Egyptians at various
times so allowing this area to stay wet might be intentional.

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Man fears the pyramid, time fears man.