The Leri is canalised for the last 2 miles of its course, and the B4353 today crosses it at Pont Aberleri. Just beyond this, it drains into the Dyfi, and at low tide you can trace its route to a location just East of Penrhyn Point, opposite Aberdyfi, where the old ferry used to come ashore. In fact this place used to be called Ferry Point, and the rusting remains of an old refuge could be seen there until very recently.
There seems to be some confusion as to the original course of the Leri, but consultation of a series of old maps sorts things out. Another bit of Saxton map of the 1600s definitely shows the river winding its way to the sea:
A clue is in a place on more modern maps called Aberleri Farm a mile to the south, and the 1890 OS map shows both the straightened Leri and the clear remains of its old wandering course, which disappears from the map in a bit of marshy ground near the sea just North of Aberleri Farm.
The 1748 chart of the Dyfi estuary clearly shows the Leri flowing into Cardigan Bay itself, just South of Moel Ynys, as does a later edition, dated 1801, which I think clinches the matter. But when was the river diverted? John Evans, Penygraig, produced a map in 1824 ("A New Map of the Vicinity of Aberystwyth") that still shows the river on its original course. Samuel Lewis's 1833 Topographical Dictionary of Wales states that the coastal area around the Dyfi was liable to flooding before the Leri embankment was built "within the last few years". Furthermore, a temporary railway line was built in 1863, from Borth up to Penrhyn Point "along the bank of Aberleri" to act as a stop-gap connection to Aberdyfi (via the ferry) when the original plan to build a Dyfi rail bridge was abandoned and the line from Aberdyfi to Dyfi Junction built instead.
I've now read that the diversion work was done in 1826, as a result of the Cors Fochno Inclosure Act, so the 1824 map must have been based upon earlier survey work.
The Leri was known as a trout stream, certainly in 1876/7, when a master from the transposed Uppingham School wrote "...groups of anglers might be seen strolling, whipping up the water to the full entertainment of themselves and the fish, or now and then blessing Sir Pryse, as the angler landed his first trout from our good friend's waters". He also records a less romantic use of the river, relating to the sanitation problems resulting from the presence of 300 boys and 30 masters at the nearby Cambrian Hotel: "...our engineers cut a duct between the Lery [sic] and the sea, so as to draw water from the river down the main drainage artery, performing twice daily [i.e., with the tide] a most effective flushing."