how long does it take for a dam to start working?

[BobThePineapple]

for a few weeks it hasnt been doing anything.

[Vandalen]

when you place a dam, you have to read the power it will get. some places do not give any power, some are awesome and give up to 2400 MW. Depents on the location.

[LinkDead]

I think it depends on the size (width), ive placed a few in rivers with short distances between each bank and i found that the wider the point you build upon the better, otherwise it may not work at all.

[Tie]

Your river needs to be moving fast to recieve power. You might be screwed though, since removing dams often causes tsunamis.

[Nixxen]

At first it overflows for a bit, then once the turbine kicks in it start generating electricity. Takes anywhere from less than a day to a few days.

You need to place it in a river with good water flow, and connect it to the powergrid.

[waterlimon]

For the dam to work, the reservoir behind it needs to be able to fill up completely (so if the dam just causes the river to redirect and flow elsewhere, it will never fill up and the dam will never work). But even if it should work, filling the reservoir can take a long time so youll just have to wait a long long time (not sure how long, few weeks?), you can visually see when its full usually (go to dam placing mode so you see flow directions, its nearly full when theres no flow in)