You will need to design a format suitable for your creek and for the people who will be doing the monitoring. You may like to establish a number of monitoring points along the creek and give these numbners or names for future reference. You may like to draw a profile of the creek at each sampling point, showing the shape of the creek bed and how the creek bed relates to banks, vegetation, structures etc. This can be measured and mapped for comparison over time eg to see how rapidly a bank is eroding, or vegetation is disappearing from the banks, and so on. Safety comes first - until you have done some analysis you will not know the chemical properties of your creek and caution is always required in handling water samples.
Water bugs are good indicators of water quality, as some are very sensitive to pollution.
There are a number of guides to identifying water bugs and knowing which ones are more sensitive and which are less sensitive. By sampling water and examining the water bugs present you will get a good idea of the water quality - a wide variety of bugs including very sensitive ones suggests that your water quality is high. Communicating what you discover in your monitoring is an important part of increasing awareness and understanding of the creek and its catchment. If you find your creek is healthy, let people know so that they can continue to protect that quality and may more readily accept your advice if that quality declines. If you find water quality and pollution problems, act on them by passing your information on to local government or State government agencies, and even on to the media if you are being ignored.