You will definitely want to bring a towel (&a rag to wipe cache!) & togs and though not necessary, it might help to wear goggles or mask & snorkel. You can kayak, swim, or walk around the lake and must take at least a quick dunk & dive to grab this cache.
When you find the cache please leave the anchor-line in place, (don't worry, it will stay floating! as there is an "egg" float attached). Unclip the cache from the line & take ashore to sign. Please check the rim is clean, dry & unbreached by any stray contents before closing the lid and take care to re-attach to the mooring securely.
* A great tip from former finders!* Bring a small float with tether & clip, and attach to the anchor line so you can easily,see GZ at the surface, to replace the cache
The cache is a yellow waterproof "GPS/phone-locker". On placement, it had a mechanical pencil, a waterproof logsheet inside a film canister, a FTF medal, a jewel, a paua-patterned pick, and a crocodile!
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I was a bit unsure how to rate the difficulty/terrain ratings, & classed it fairly high due to being underwater. Having said that, it should be fairly easy to grab & is visible from the surface; so fingers crossed that it doesn't get muggled! ( 10+ years & still unmuggled- yay!)
Generally you should not look out of place as Waro Lake is a popular spot for swimmers; and more! 
I have seen swimmers, scuba divers, kayaks, sailboats, windsurfers, radio controlled craft, waka-ama, dogs & horses making good use of the lake. The Whangarei Tri Club trains here on Monday evenings, and the high rocks & swimming hole between this cache & (GC12XB8) "Waro, Waro Could That Cache Be? " are a very popular jumping/diving spot 
Give it a go! 
The reserve is now dog-friendly! Many improvements have been made to the reserve; it is now fenced off from the adjacent properties, has a nice track which goes all the way around the lake and several new benches & picnic tables along the shore.
When you are at the NW end of the lake, looking from shore towards the water, at the far right there is a small rock outcrop jutting out (above water, but may be hidden amongst the grass); beyond that to the right, the lake edge is full of reeds. If you stand on the outcrop and look across the lake towards the dock & toilets, the cache is in this line of sight & about 10 meters out, and only about 2 meters away from the reeds. Sometimes, in perfect glassy conditions you can even glimpse the cache! You can even see these features on Googlemaps if you zoom in on satellite view! Note* Waypoint added for the outcrop * You can easily dive off into clear water from this outcrop & glide right to the cache. Alternatively, further to the left and in front of the whitish retaining wall rocks, there is an ample ledge just under the water; some may find this a more convenient easy entry into the water. If you struggle to safely replace the cache as found, Please proceed to https://coord.info/GC906RY "Waro Rocks V2", stash it with the cache there & let me know about it. Thanks!
summer is not over summer is not over summer is not over! LOL