You will need green, blue, and brown worsted weight yarn and a 3.5mm hook. At the end of each row chain 1 and turn.
Begin with 25 Foundation Half double Crochet in green yarn. If you need any help with Foundation Stitches please refer to this post where I provide a detailed tutorial.
Make a total of 4 rows, including the foundation chain, of HDC in green.
Make 8 HDC in green. On the last pull through of the 8th HDC, pull up blue. Make 9 HDC in blue. On the last pull through of the 9th HDC, pull up green. Finish the row with 8 HDC in green.
For rows 6-8 make one additional blue HDC and one less green HDC on both sides.
Row 6 7 green, 11 blue, 7 green
Row 7 6 green, 13 blue, 6 green
Row 8 5 green, 15 blue, 5 green
Row 9 4 green, 17 blue, 4 green
HDCx4 green, 17 blue, 4 green
For rows 13-16 make one additional green HDC and one less blue HDC on both sides.
Row 13 5 green, 15 blue, 5 green
Row 14 6 green, 13 blue, 6 green
Row 15 7 green, 11 blue, 7 green
Row 16 8 green, 11 blue, 8 green
HDC in green
Embroider mud bank
Change to a larger hook, I've used a 5.75 mm here. Insert your hook through the fabric at the edge of glue and green. Yarn over with brown on the back side and pull through to the front side of the fabric.
Slip stitch along the edge of the blue, making small angles wherever possible so that it is not a perfect circle. Once you return to the beginning, remove your hook from the loop. Insert your hook from the backside to the front. Catch your loop and pull it to the backside. fasten off.
Make pond grass
Wrap green yarn around 3 fingers several times. Make one cut in the middle to make several strands.
Fold one strand in half. Insert your hook through a stitch on the fabric. Catch the middle of your folded strand and pull it through partially, so that the loop is on one end of the fabric and the loose ends on the other. Yarn over with the loose ends and pull through the loop.
Repeat until clumps of grass are desired fullness.