Aquifers from oceans will end at a very short distance compared to aquifers in rivers. Rivers usually generate between weirdness levels of around -45 to 45, while their aquifers extend to weirdness levels of around -300 to 300, creating an aquifer distance of about 255 weirdness from the actual river. Oceans usually end at continentalness levels of around -185, but their aquifers end at continentalness levels of about -150, creating a mere distance of 35 continentalness. That's even shorter than beaches, which end at a distance of 85 continentalness from oceans; this causes very ugly aquifers to generate in between beaches.

To reproduce, use the seed 947651566 and notice that at the coordinates -34 64 25, 60 64 -55, and 104 63 83, the aquifer extends a decent distance from the river. However, at 1864 62 -3461, the aquifer extends so shortly from the ocean that it completely shatters a beach.