Bird ID. Northern Pintail, or other?

Hello. I was wondering if anyone could ID this bird sound for me? The recording was made near some reeds beside South Mere Lake at Thamesmead, London. I couldn't see what birds were making the sounds as every time I got too close they would stop. The only birds I saw were Canada geese, swans, coots, and what looked like Great Crested Grebes. (Apologies for the construction sound you can hear in the background.) I tried a bird ID app called Merlin and it initially suggested the Northern Pintail but it gave no confirmation on subsequent attempts, and I didn't see any at the lake. Many thanks for any tips.