Some of the diving possibilities around there:
Pulau Talang Talang lying off the mouth of Sematan River is a protected turtle sanctuary for green, hawksbill and olive ridley turtles. The Katori Maru is a world war II shipwreck located about 50 km from the mainland. It was a Japanese troop carrier which was sunk by British aircraft. The wreck is not covered much and visibility is poor at 5 to 8 meter.
The sea, sandy beach, the sun, the breeze and sound of pounding waves have always lured city dwellers.
One such place which has been attracting people is picturesque Sematan, a one-and-a-half-hours drive at reasonable speed from Kuching, going through some of the most striking terrain of Sarawak.
From Sematan, you can see the turtle islands of Talang-Talang Besar and Talang-Kecil. On calm seas, you can get there by jet-ski in less than 15 minutes. Further off is the Island of Satang Besar which cannot be seen from Sematan but is in full view from Santubong. These are protected islands. Permission is needed to visit them.
We did not find any dive center in Sematan, so we recommend hiring the gear in Kuching.