It might have a small effect on the local humidity but in general reservoirs and canals are not big enough to have any measurable effect on the climate, even locally. So it might have some very small effect by increasing dryness in plants or soil on the shore but the amount of evaporation is so small it wasn’t really adding to rain in any meaningful way.

Even the Great Lakes, large as they are only have effects in small, downwind regions, and the weather returns to what is typical for surrounding areas before you get far. And they are hundreds of times larger than even large reservoirs. Only the oceans are big enough to affect weather globally.