I have a 2.5 acre pond that was built around 1993 as part of a golf course. I bought a house which has a section of the pond, including the dam and drain on my property in 2005. We have had a lot of rain this year and after a recent heavy rain the siphon is barely flowing, even though the pone level is about 2 feet above normal.
I need to mention that it appears that the trash filter on the intake is either damaged or missing as I have had catfish sucked through the drain. That said I assumed the drain was clogged and used a 100' 5/8" electric snake to clear the line, but still no luck.
How do I get the siphon restarted?

Hi big-daddy,welcome to the forum.That said,how big is your pipe?Is water flowing through at all?You can do a couple of things to get it started.If you have flow,put a turn-up pipe on the down side to stop air from entering the pipe and it should selfstart the siphon.Or you can pump water up the downside back into the pond and get it started that way as well.Make sure you dont have any air leaks in the pipe and you shouldnt have too much trouble getting it going again.

Sorry, I'm new to this. What is a turn up pipe and which side is the down side.

Its an 8" drain and there is a small flow, the pond level is above the siphon vent.

There are other siphon experts on this forum to guide you thru this, but my $.02 is simply to beware and respect the power of the suction if/when the siphon kicks in. Even at 8", it will suck the skin right off your arm. (well, maybe not the skin, but your cuticles and nails will be bye-bye)

Thanks for the feedback, normally when the water level is up like this the discharge pipe blows out the water like a fire hose.

Your pipe is clogged. If water is obviously being sucked hard through the siphon vent, the clog is on the pond side of the pipe. If very little water is going through the siphon vent, the clog is on the downstream side of the pipe. If you can determine how hard the suction is through the siphon vent (since the water is 2 feet above the pipe), you can decide how best to attack it. It's not unusual for a turtle to get stuck in an 8" pipe at the bottom of a pond. If that's what happened, your vent pipe will have maximum water flowing through it and just a trickle coming out the back side into the creek.
The only way a siphon won't work in your situation is if the pipe is clogged somewhere.

Be VERY carefull using a drain snake from the outlet into the inlet side. We recently had a member barely avoid a catastrophy when the plug was cleared. The spinning cutters on the snake came out with the water and cut a couple people, IIRC.

Thanks, I believe its a turtle also as one or two have come through, just don't know why the snake didn't clear it.

Are you sure the snake was long enough? A siphon is a lot longer than you would think.

You may want to try to cap the outlet and fashion some sort of connection to use a trash pump to pressurize the pipe and force out the blockage. Bad thing is, it may re-plug after in starts again.

big-daddy, I think what Tom was describing was putting an elbow on the outlet side and attaching a stand pipe to it so it is taller than the pond level, then pump water into the pipe so when the level in the stand pipe is higher than the pond the pressure will back-flush the clog out.

But I could be wrong.

Rainmans fix would do the same thing.