anything "negative" about having a deep pond?...

[moikoi]

what do you think is the ideal depth?

[PapaBear]

The deeper you go the better your design must be. Deep ponds are difficult to clean manually, so design it well with properly placed bottom drains, air domes, tpr's, etc... so your in-pond maintenence is minimal.
Downside issues I can think of would be difficulty in netting out a fish you want to take a closer look at. (sick ones tend to hang alone at the bottom quite often). That means you would need an extra long handle on your net and/or a deepwater seine.
Upside is a much longer list. Deep ponds (6'-10') have fewer temperature issues year 'round, promote outstanding body development, and frustrate the living daylights out of predators.
I'm sure others will chime in with things I've overlooked.

[MikeM]

It depends on your goals. Anything deeper than 4 feet results in the loss of "intimacy" in viewing the koi. There is a consensus among the most skilled keepers that deeper than 4' is best for development, at least for koi genetically capable of growing over 24", which is most all of them. Depth in the 8' to 12' range requires special considerations on equipment, etc. Over 12' deep raises lots of issues. I don't think any hobbyist needs to go there.

[dick benbow]

6-7 feet is best. Addresses all the pre-mentioned concerns, allows for strong internals, and for those of us with cold/winter issues it buys us with depth volumn the opportunity to avoid any sudden change in temperature. even with an inside pond where heat retention/chilling is not so much of an issue
the depth is still required to get the best growth body shape from your koi.

[moikoi]

i think 7.5 ft is perfect.i seen a 12 ft deep pond,too deep!!

[mynamy1]

Deep pond needs better water clarity than shallower pond to look as good. Make sure your mechanic filter is excellent. Well, if X and Y are limited what else other than Z? MALe

[dcny]

I would imagine that it's harder to catch koi in deep ponds.

[koikiller]

better have a fence before some 6 year old kid decides to go swimming in it

[Birdman]

Both my ponds present and in the past (12,500 & 40,000 gal) were 4 feet deep and wide. Wider than what you could catch fish with a pole net. My water stays cold, at least colder than what is comfortable to wade in. I purposely made these ponds 4 feet deep because for me that is chest wader depth. These are out door ponds subject to all sorts of stuff getting blown in. Several times a year I find my self wading in it to do something. Just something to think about.

My new indoor pond will be a totaly different inviroment, 9 feet by 18 feet but 6 1/2 feet deep. No plants or decorations, just a dedicated koi pond. I made it as deep as I could knowing the fish were reachable with a long handle net.

I think a person needs to think about what the purpose of their pond is for, where it is going, how it will be maintained and then go from there.

[aquitori]

I think the 7-8ft is a good depth.