John Marston arrives in Blackwater at the start of Redemption by using the Morningstar to get across the lake.
In Redemption, if the player looks across the lake from Blackwater, they can see that Nuevo Paraíso and Lemoyne appear to border each other. This is not the case in Redemption 2. This is due to the fact the Lannahechee River had yet to appear in the Red Dead universe.
In Red Dead Redemption, this location does not count towards 100% Completion.
In Red Dead Redemption 2, players can find the Tricorn Hat inside a shipwreck in the cove of one of the small islands at the eastern side of the lake. A lockbox there also contains Aged Pirate Rum.
As of the PC release/1.15 update, the Cat Eye Trinket can be found on southernmost island.
Flat Iron Lake in Red Dead Redemption 2
Flat Iron Lake in Red Dead Redemption
Flat Iron Lake viewed from Clemens Point in Lemoyne.
Flat Iron Lake on a loading screen in Red Dead Redemption 2