Detailed Instructions: In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Problem:Passage: Larrys Creek is a 22.9-mile-long (36.9 km) tributary of the West Branch Susquehanna River in Lycoming County in the U.S. state of Pennsylvania. A part of the Chesapeake Bay drainage basin, its watershed drains 89.1 square miles (231 km2) in six townships and a borough. The creek flows south from the dissected Allegheny Plateau to the Ridge-and-valley Appalachians through sandstone, limestone, and shale from the Devonian, Mississippian, and Pennsylvanian periods.
The valley's first recorded inhabitants were the Susquehannocks, followed by the Lenape and other tribes. The Great Shamokin Path crossed the creek near its mouth, where Larry Burt, the first Euro-American settler and the man who gave the creek its present name, also lived by 1769. In the 19th century, the creek and its watershed were a center for logging and related industries, including 53 sawmills, grist mills, leather tanneries, coal and iron mines. A 1903 newspaper article claimed "No other stream in the country had so many mills in so small a territory". For transportation, a plank road ran along much of the creek for decades, and two "paper railroads" were planned, but never built.
As of 2006, the Larrys Creek watershed is 83.1% forest and 15.7% agricultural (a reforestation of land clear-cut in the 19th century). Nearly 9,000 acres (3,600 ha) of second-growth forest are protected public and private land for hunting and trout fishing, with more land protected in parts of Tiadaghton State Forest. Pollution from past industrial use is gone and Larrys Creek "has an exceptionally scenic, ultra-highwater, whitewater run" for canoeing.  Despite agricultural runoff and small amounts of acid mine drainage, water quality is quite good, and a water filtration plant on Larrys Creek supplies over 2500 customers.
Solution:
What type of transportation was planned but never built in the creek that has a water filtration plant that supplies 2500 customers?